The real question before I ever pick one is to find out what the individual instrument sounds like. Some are strident, and a bit bright, others woody and very mellow - some seems to be very wheezy, and other just dull. My soprano has got shriller as it has got older - it's about 25 years old and wasn't a classic. This makes a nice dynamic work quite nicely - Oddly, those Sennheiser guitar cab mics - the square ones are quite nice on it, but they don't record my alto very well. Sennheiser 421 suits that, or something like an RE20 for dynamics, but for a condenser, something a bit more mellow is needed - TLM103s are a bit over bright, but an old Oktava 318 is quite nice. AKG 414 or old 451 mics seem to like my tenor, but so does an SM57?
I know my instruments well, but recording somebody else means my usual choices are often wrong. The 414, for example often captures the clicks and clacks of the keywats and pads quite nastily if the player is a fingers off the keys type.