Action shots, portraits, landscape and scenery

Sony A57 beats Nikon right up to (and including) the D90 hands down. Go for it. You wont be disappointed. The Electronic Viewfinder in Sony is good, however, slightly grainy in low light.

If you're looking at the D90, you can also check out the A-65 from Sony. It has an OLED Viewfinder which works great

nikon is always rated better in most terms over - however also try to check the later releases like d5100 or d3200 as they would be cheaper and easy to adapt before targeting a leap for ful frame

The electronic viewfinder in Sony a57 is the smallest LCD in the world!