I went throught the same thing, wondering the same questions..
I went to Cabela's and they had a chart there and the brands and models that fall into what you are looking for.
Might be the best idea for you to go there (if possible)
I got one with a vibrate, mile range, and was small and light weight, rechargable, expandable to a couple of dogs.
Think of what you want it to do, and then pick the one that fits that bill,