Why would you select the A99 over the D800 or 5D MKIII?

Frankly I don't see any reason in your description why you shouldn't go with Sony.

Id say go with the a99. If not the D800. Sony is creeping up in the photography world little do people know and are already becoming the new Kodak with there image sensors being in many many diffrent devices already (Ironically and coincidentally, the Nikon D800... yes, you read it corectly, the D800, iPhone 4/4s and 5 to start) and they are the real major innovator in the photography world at this moment. Moving forward, for lenses, Sony does actually have a decent array of lenses and Minolta AF lenses also work with all A-mount lenses. From what you have stated, you should be just fine with Sony's Array of A-mount lenses. Wile it's understandable why everyone choses Canon and Nikon (There great! I understand!) Sony is also a great camera maker as well and should also be considered just as much as Canon and Nikon as, everyone always says "Go with Canon" or "Go with Nikon" and tend to be afraid to suggest others try something new and different and to go with Sony, when Sony is really in all honesty, a great camera maker, always gets labeled as "the odd camera" and deserves more attention from photographers. Do not be afraid to shoot Sony because they take a different route from Canon and Nikon, it's actually quite alright and i think you'd agree with me. For the record, i recently bought an a57 just about a month ago and from my experiences with it, Sony's STL line more than competes with Nikon and Canon's offerings, it innovates.

A faster camera between the three

Lightest of the 3

AF range control and new AF-D mode

Same price as the D800 and cheaper than the 5Dmk3

I'd say pick which ever feels best to you. I am a Sony shooter and have never had any problems with their cameras at any time. I mainly shoot weddings and portraits and have not really been hindered by ISO 3200 and up if needed. The A99 is a step ahead compared to the A900 and so it may warrant a look on your part. As far as Canon having superior glass I would say not. I have shot with their L lenses and they are not better than an equivalent Zeiss or Nikkor lens. Having more lenses is fine, but how many focal lengths are you attempting to cover. Sony has all of the major ones checked off and have quite possibly the best 85mm/f1.4, 135mm/f1.8, and 24-70mm/f2.8 lenses available for full frame. The 70-200mm G lens definitely holds its own as well. Instead of just taking our suggestions, bring some CF cards and SD cards to your local dealer when all are available and take some test shots with comparable settings. Stick them in Lightroom and judge for yourself which appears better to you and which needs more processing time. Either way, you should be happy with whichever you select. Most people seem to pick a certain brand to justify their purchases to someone else thinking you are supposed to have that brand. I no longer have anyone asking why I shoot with Sony instead of Nikon or Canon. 

*Amazing image quality - check dxomark.com scores - d800 is top sensor quality-wise

*AF assist for shooting in low light without flash - 5d m3 does not have that

*Amazing quality low price line of fixed primes - 50mm 1.8G AF-S, 85mm f/1.8G AF-S, both excell their twins of other brands by quite much in fact.

*Uncompressed HDMI output if you're ever to jump into professional movie/video production

*with all of these amazing characteristics it's still the cheapest option :)

I have been seeing in various places about green tint on the Nikon. The amazing ISO works wonders, but because of extra resolution, aliasing and moire can be a problem. Also, video can suffer because of high pixels.

Canon is a good all around camera (not really stellar in anything, but excellent and balanced), but cost is a factor. As others have said, how many lenses do you need? You can get as many as you want with Canon. The general ecosystem on Canon is better (if you ask randomly for a camera accessory, you will probably get a Canon, with Nikon a close second). Having less megapixels helps with video (if that is a consideration. If not now, it will be a necessity soon).

Sony has all the bases covered on lenses, and they are of top quality. It is pretty much the Canon in another body. It is the only one able to shoot 1920x1080 video (again, if that is important right now) at 60 fps. The Sony camera is bristling with new technology and is poised for continued innovation . It can do pretty much what the others can do and has a few tricks up its sleeve. They have come a long way in a short time and the company looks financially alot better. They also have top quality micro cameras if you need a backup or a walk around camera.

In the end, if you are against an EVF, you only have two choices. For your situation (weddings, bars, portraits, etc.), if you can't handle an EVF, I would go Canon. If you can, go Sony.

I have 550D and a few L lens and also Sony A77. Normally I use for some event, travelling and macro shooting. I also want to upgrade to full frame so I am waiting a few years for new FF model. But when I see the new 5D, the drawback for 5D no AF assist. So it cannot focus in dark situation. It also has no flip or articulated  screen. 

Even my A77 has no problem with that. When comparing 550D and A77, seems Sony is more fun. A lot better in focusing and expose control in moving subject either in still photo or video mode. WIth build in HDR/DRO,GPS, build in SteadyShot, multishot noise reduction, panorama sweep, there are many features. I also like the EVF. No more overexpose/underexpose because WYSIWYG. The dynamic range and metering system is a lot better. No need to use CPL filter. I can also use the HSS flash even if I mount it in the body hotshoe.

So my choice is A99.  With new invention AF range and dual autofocus system definitely will help me better, Compare to Canon is very slow in inventing new features. So in a long term I believe Sony is the best for me to stay with. The only where 5D is attract me is when shooting ISO above 6400 but not much different compare to A99.

I just need 5-7 lenses, Zeiss and Sony G lens are enough for me. Some are better compare to my L lens.They can be used with NEX mirrorless camera and camcorder with AF also.

I've used the a55 the a77 and decided to buy the a99. I've enjoyed to the electronic viewfinder never finding it to be a hindrance. I've done landscape, portraits, and photojournalism with the sony line. There might not be a ton of lenses but having a strong line of Zeiss lenses is pretty cool. Sigma also makes great cheaper lenses for sony a mount. You can look at some photos in the link bellow that I've taken with the a55 and a77. Also just to note and I don't hate the other brands, and its funny because I usually go out to the desert with two other guys one shoots nikon the other shoots canon. Everyone comes back with awesome pictures. Just a little bit of sony props though that they are making the sensors that most cameras are using now days.

http://www.viewbug.com/member/trevortoma 

You can't go wrong with any of these cameras as they are all very good tools. It comes down to each unique strength, I was a Nikon shooter before the NEX 7 came out and I fell in love with the EVF, it just make photography so much easier or say user friendly with all those information and focus peaking. Weakest link will be lens, not saying Sony lack quality lens but they lack the likes of the F1.8 budget lens Nikon offers.

D800 most likely will have the best IQ of the three but the 36MP files could become a headache if you shoot a lot, it will best suit a landscape or studio shooter.

The 5D3 probably has the best AF system between the 3 but for your use I think it's an overkill and having the worst DR does hurt the Mark III.

I would also consider the D600 if I were you, together with the latest F1.8 lens from Nikon, it's really a bargin.

Great choices all three, but why not consider also the Nikon D600?

I would pick the 5D Mark iii or D800 over the A99.  Don't get me wrong, I don't have anything against Sony.  I own one myself.  I'm just not at all a fan of the electronic viewfinder.  It sucks your battery life.  Snapsort claims 500 shots on a full charge for the a99, 900 shots for the d800, and 950 for the 5D Miii.  Plus I just think that there's no real replacement for a good ol' optical viewfinder.  The only electronic viewfinder I've actually seen was the one on the a55, and even though I'm sure the a99's is superior, I would still stay clear of it.  And just like everyone else is saying, the lens selection for Nikon and Canon is definitely better.

I was really leaning towards the Sony but the more I looked into it the more I steered towards the Nikon.

The Sony doesn't have nearly as many lenses available for it.

Also, the digital viewfinder became a concern to me, I really want to stick with something  that has an optical viewfinder.

I'm not sure on what you are looking to spend but I put together packages based off of retail pricing and with getting the body, 3-4 lenses, speedlight, extra batteries, vertical grip, remote and other minor accessories both of them ended up at nearly the same cost. So with a full package in mind I think the D800 pushes even further ahead with the great lenses Nikon makes.

Also the speedlight and Nikon's iTTL system is top notch.

Sony's sort of the odd one out of these 3 brands.  Their ecosystem is much less prominent in the photography world.  I'm a Nikon guy myself, but would recommend the 5DIII in this scenario.  Based on what you've said, it seems like you wouldn't have a use for 36MP.  Because of that, I say go for the more nimble 5D and its immensely popular ecosystem.  

I own a Canon 60D as well, but after reading some opinions on the internet by the guys who really understand, I think I would go for the Nikon. D800 seems to have the best FF sensor in the market today, regarding signal/noise ratio. The issue is the lens price. Nikon historically has more expensive lenses than Canon, but since the D800 body is cheaper than the 5D3, it would not be a problem. What regards Sony A99, I don´t know anything about their DSLR, but I would aviod them just because they are pretty new in the market...