Lancer Evos and anything with good paint. So far I have every Evo, but I'm considering a second set for painting colours other than Scotia White and tuning. I also have around 3 or 4 MNP III Skylines, two MNP II's, three 2002 Turbos in Taiga Green Metallic (a great colour for wheels) and the 70's Civic 1300, I'm pretty sure I shouldn't like that orange, but I do. Also, painting any Honda in Championship White instantly increases the horsepower by about 40. That doesn't actually happen, but they do all become much faster looking thanks to the Type R association.
I'm also buying every premium, I don't have many left, now, but they are the most expensive. I have a lot of Super GTs left, a few NASCARs, the R10 (which I'll try and win... Maybe), one 908, the 787B, the classic Le Mans, the Miura, Ferrari F1's and... I think that's it. Still, that must be over 100 million credits' worth. After that I move on to the standards.