Yes there are lots of things to consider.
For me the main factors include (in no particular order):
* mileage earning on usual routes/class of travel
* mileage burning - great earn rates arent much help if awards are ridiculously expensive
* lumping these together is probably best - ie how many trips on a typical trip does it take to earn an award you'd like to use
* award availability
* special services available to flown carrier's elite - includes free upgrade vouchers, better seating etc
* ease of (re)qualifying elite status
Of course others may (and do) disagree!