I liked GT2 because it had 400+ cars and most of them were race modable. Hated the fact you could only have 100cars. Had to sell many full race spec cars just to 100% complete the thing.
GT2 has more custom cars. I like the part that you can mod almost all the cars. I wish they had the RUF CTR 2 Sport! This RUF had more wider fenders. =)