wrx is a 5-speed, sti is a 6-speed. the sti transmission and engine can both be swapped into a wrx fairly easily. reliability is all up to you. what do you want to do with it? if you are fairly conservative on the mods it will last as long as you want it to. start making a lot of power and you will start breaking a lot of shit, just the same as any other car. The wrx responds VERY well to bolt ons though, and the boxer engine makes a lot of torque as compared to most inline 4's.