MK6 GTIs had issues with a cam follower and high pressure fuel pump going bad every 50k miles, IIRC. The PQ35 platform are not bad cars, but for similar $$ the MK7/MQB platform is a significant step up. The Gen3 motor is pretty robust. Not that I'm suggesting throwing a big turbo on it, but guys are getting north of 600hp on the stock bottom end (and head!!!) after going big turbo and supporting parts/fuel/tune. The amount of boost safety/predetonation safeguards built into the stock ECU is impressive. If you look at logs on some of these 30+psi cars, you can see the ECU pulling timing on individual cylinders mid cycle, which means there's very, very little chance of seeing major engine failure due to knock or high cylinder pressures, which means, no bent valves, or rods windowing a block, or head lift blowing a head gasket. Anyhow, if you can find a GTI S with the Performance Pack, you get the same brakes as a Golf R and an electronic limited slip diff that actually works. Another car I'd put on your radar that can be had in good shape for $15k-ish would be BMW 135i - really great engine, great chassis. A lot of "purists" would say the 135i is the last of the great driving bimmers, even if the turbski N54/N55 isn't in line with what a "real" bimmer supposedly is. Buddy of mine had a 135i and it was an absolute hoot to drive.