All year wrx's have shit trannies, best year is 05, has the revised syncros and etc, 06 wrx is the best year WRX hands down. 2.5 liter, Aluminum LCA's, 4 pot brakes, and a workable ECU with no hidden bugs unlike the 07's. If youve got the money, Buy An EVO hands down. Much better bang for the buck and if you wanted to take it to the next level its not gonna cost that much. If you just want a nice daily then hell get a Suby there nice cars. $500 can get you in the 12's with an 06.
Things that were mentioned which are incorrect.
#1: If you buy an 05 wrx you basically have a "RA" gear set which is nothing but the JDM 5 speed Sti. The gears are still shit and will brake as quickly as stock.
#2: VF43/VF39/VF34 are practically the same exact turbo, one will not be ANY better then the other, if you get a WRX buy the cheapest one you can find, expect around 320whp (With an 06WRX) Probably 290-300whp(with a 05-02) Even though supposedly a Vf34 spools slightly quicker then a Vf39(Us Spec Sti 04-06) And the VF43 has a better more controllable wastegate (07 Sti's and up)
#3: Any 2.0liter WRX is going to leave you wanting more. You have a Crappy Engine that will pop at 350whp, You have no TQ, the heads are shit, and the transmission is still weak as hell. If your going to get one buy an 06!

Just dont buy a Sti, there a waste of fucking money =\. Just drive each one, a 2.0liter wrx, 2.5liter wrx, An STi, and an EVO. Compare, decide. Just know 02-05 wrx = Crap tranny, crap engine, Have to buy an Upipipe,Downpipe,Catback,Tune,injectors,Turbo,Fuel Pump,Intercooler etc etc to run 12's. 06 Buy a Downpipe, tune it run 12's on meth/race gas. Or just buy a downpipe an Sti turbo and tune it and you can get into the 12's on pump with your stock intercooler running around 16psi (which is fine for the stock topmount)