Pros- Cheapest car of the 3,AWD,Pratical 4 door,smoother ride than the STi,lots of mods
Cons-not as powerful as the STi, transmission is a bit nothcy and handling is ok, insurance can be expensive
Pros-AWD, 300hp and ft/lbs, AWD 4 door practicallity, handles well, lots of mods
Cons-ride can be harsh insurance is expensive, overall cost is expensive
Pros- smooth V6 (very different than the turbo feel), nicer interior, arguably the best looking of the 3 (if that matters to you), nice transmission, Basically just more luxury. Insurance will probably be less (I'm guessing since my Z costs less than my WRX did)
Cons- not as fast or powerful as the STi but costs just as much,not as easy to mod.
So basically it seems you have the luxury option (G35) the performance option (sti) and the cheaper more toned down option (WRX)