trying them out side by side is always the best, but can be very inconvenient for a number of reasons.
my strategy is to buy used, that way even if i don't like the mic, i can generally sell it for no less than i paid (often times i will even make a few bucks in the process).
do lots of research by searching old posts on these message boards. you can learn a lot about these mics just by reading other people's opinions.
good luck on the search.