I think aerobars are kinda like saddles, that you'll find lots of different opinions.

Are these to go on a road bike? If so, I've found that it's important to have arm rests that can be positioned back of the handle bars. Personally, I like bars that are adjustable for width and that the bars are adjustable for angle. I like the "ski bend" shape, but the S, or straight bars are all the trend these days.