I have seen the r32 and the s14 as the two most common ones. Are there any other major ones?
Honestly, if you look close enough, it's pretty much the entire roster of the first 4 (motorsports) games. Ones that are particularly bad, for me:
Subaru 22b (still bad as of FH5)
Ferrari F355 (still bad as of FH5)
Ferrari F40 (fixed at some point)
Honda NSX (fixed at some point)
Lamborghini Countach (still bad as of FH5)
Ferrari 246 (still bad as of FH5)
TVR Sagaris (still bad as of FH5)
Acura RSX (still bad as of FH5)
Acura Integra (fixed at some point)
BMW E30 (still bad as of FH5)
BMW E46 (still bad as of FH5)
Chevy Chevelle (still bad as of FH5)
All of the old Corvettes (still bad as of FH5)
Honda S2000 (still!)
FD RX-7 (still bad as of FH5)
FC Rx-7 (fixed at some point)
350z (still bad as of FH5)
370z (still bad as of FH5)
996 GT3 (still bad as of FH5)
Golf R32 (still bad as of FH5)
In the first two games it was sort of forgivable and honestly wasn't really distracting considering the relatively low fidelity (mesh and resolution) of the game overall and the kind of smudgy/bloomy presentation. But as the games got sharper and more photorealistic in their presentation, and with the laser scanned assets brought in later, the poorer assets have become really distracting.