I got both. I loved Hot Pursuit 2 on PS2 as a 'pick up and have a bit of fun' game, HP3 doesn't quite cut it in the same way for me. Have to unlock every car, albeit it easily.
GT5, I haven't played enough to have a solid opinion on it, been a GT fanboy since the beginning, bought Forza 3 to fill the void, really liked that, but GT5 hasn't convinced me totally yet, but like I've said, I've not played it enough. I don't buy a lot of games so I know I'll play GT5 a lot now I have a bit more free time and will play HP3 a fait bit too.