I fully agree with ScottA on this opinion. I love the Billy much more as it has the variety of programs and makes you reach the orgasm much quicker then Aneros. I guess it's the best to try them both to figure out.
I have chosen a couple Aneros models. They are a smaller up front investment and can be used during sex without ass-istance (sorry, couldn't resist). Vibration would probably be fun, though. Maybe someday, but not my initial choice.
First off i haven't tried either. I hear the arguments for the aneros but i am currently more keen on the billy mainly to get my own luxury to with a vibrator in the end so that I can stimulate the prostate more directly.