It makes me wonder though, if someone came to PC2 without trying GTS at all, would they get used to the game and physics easier? Does GT in some ways "spoil" PC2 for people? Hmm.
I would say GT (especially versions 5, 6, and Sport) spoil people into believing how to drive a car on it's limits. As someone that has raced my own car and karts in competition in real life, GT doesn't shed the most realistic light on how physics and driving dynamics work. PC2 is closer to reality.
Yet back to the OP - Both are great games for their targeted audiences. Using food analogies: GTS is a grab-n-go, easy to consume experience. While PC2 is a highly customization experience (from simple to complex/nuanced). Here are some of my observations.
1 -
How much realism do you want? PC2 wins
2 -
How much time are you willing to invest in car setup (yet there are two defaults for each car - Loose and Stable, so you can hop in and go). GTS wins if you want to hop in and go. PC2 wins if you like to adjust the car for your driving style so you can go faster.
3 -
Online racing - GTS probably wins as there's more people playing (I haven't taken a look at PC2 online lobbies yet).
4 -
Graphics - GTS is very polished, very little adjustments needed. PC2, depends on how you set up the visual effects.
5 -
Sounds - PC2. GTS still uses a lot of generic effects, and muted or over amplified sounds
6 -
Tracks - Yes. lol. If you want to drive on real life circuits, PC2. All of them were laser scanned, so every aspect of the track is how it is in reality. GTS has great tracks too, yet most aren't real. So this is really subjective.
7 -
Offline racing - In PC2 you can adjust how aggressive and how smart the AI is. So this will vary. GTS - same train of cars that are too slow.
8 -
Car Damage - PC2 you can modify it to how you want. GTS, damage is not encouraged. lol
9 -
Track Penalties - PC2 - gotta keep at least 2 wheels on the track at all times (unless you turn this feature off). Otherwise, you'll get your laps not counted or time penalties by the race director. GTS, they're extremely lenient.