What phone would be good for internet and YouTube?

The Nokia Lumia 900 would be better for web browsing, but as for watching youtube videos, the blackberry would be a better solution. The keypad and trackpad on the blackberry isn't the easiest or the fastest way to browse the web, but the screen on the blackberry is much more crisper due to the high PPI, which makes it a good youtube experience. (284 PPI vs 216 PPI) If you plan on showing people a cool video on youtube though, I recommend the Nokia Lumia 900.

In the end, it comes to whatever else you plan to due on the device.

If you plan to use your smartphone for work, take the blackberry without a doubt, but if you want to use your smartphone as an all-around phone, take the Lumia 900.

I personally think the Nokia Lumia 900 is better because of it's growing app store, and easy-to-use interface.

This phone is faster than both of those phones combined

The Nokia Lumia has 4G access, which the BlackBerry Bold does not. This would translate into quicker download times depending on what kind of cell service is available to your area. The Lumia has a bigger screen which would make for a much more pleasurable YouTube viewing experience. 

Nokia Lumia would definitely be a better option for web browsing and youtube. The blackberry devices are too slow for web browsing and it takes too long to buffer videos even with the 3G access.