From what I've seen most STI owners upgrade the front before the rear. I usually get the biggest adjustable bar available and go from there. I'll let STI owners chime in. A lot of it is going to depend on your drive style and whether or not you're going to be autox/track racing
Strano makes a 32 mm hollow front bar, however it's a bit exterme unless you are going to autox. The must popular would be the whiteline adjustable 24mm solid bar for the front.
Oh, I guess for the STi is opposite than the WRX. I've always heard to stiffen the rear sway bar to correct understeer. Please correct me. I'm a little confused.:eek3:
The front bar is for better turn-in.... not really correcting the problem of understeer. Most people upgrade both bars at the same time, however is you run stock class in SCCA you are only allowed to replace the front bar. While the strano bar didn't help the terminal understeer it greatly improved my car's turn-in speed and reduced body roll. Personally I've have joined the "strut" camp for the "strut versus sway" discussion, my ohlins have corrected many of the issues that caused understeer in my car.