to help narrow down your options what sort of fishing will you be using it for most, ie. salt vs fresh etc. and what do you want it to do for you. Other than that you would want the best resolution (pixels on the screen that your money can buy) this takes alot of the guess work out of the images and lets get a better picture of what the fish are actually doing (how active they are) so you can match your technique to the fishes mood.
Cheers
Simon.