most of the higher end regs perform close enough to be compareable. here are some things to consider when purchasing.
cosmetics (important to some)
weight
height/length
replaceable macro fitting? (some are not replace able. like a tall CP reg for example)
range (CP's for example are HP or LP so be sure to select the correct one)
adjustment (some use a ball bearing, others use a spring. also how easy is it to adjust? does it have a lock nut like an evil detinator?)
and the most important factor for me... it has to have the macro on the bottom! I can not stand to have the macro on the side or middle of the reg, such as a torpedo. Great reg, but I will never use one willingly. (others may have the exact oposite opinion.)
my .02. think about what you really want in a reg, then you can eliminate all the ones you don't want. all suggested so far are more than adequate. personally I love the sidewinder.
good luck!