Shield 9 here.
Price, reputation, slim... my main reasons.

Like most though I have become more of a gun nut and would like others. I've got a p238 which I like because it is smaller than the Shield.
The Shield 45 just became available in MA and of course I'd like to try one out. I held a 9c and it was wonderful... wouldn't mind one of those. The list goes on. LOL
One of my friends has a H&K VP9 and that shoots great for me. Another one just went through his carry class and is settling on the H&K p30sk.
Best option as someone stated already, find a range to rent them and try as many as possible.