My favorite so far is easily my customer's E39 M5 that I've been restoring for the last year. We had a high output engine built by Partee Racing mated to a diffsonline race prepped transmission. We recently got it dialed in on the Dyno and the thing is a riot. As far as current gen cars go, the new i4 M50 is an amazing car, as is the new i7. The i4 is just stupid fast and nimble, whereas the i7 is a big luxury boat with more tech squeezed into it than you could imagine. The new M cars are cool, but they don't do a whole lot for me. They feel too numb for what they're supposed to be. At least with the i cars, being electric, I expect them to be more numb and reserved feeling, which they are. But it doesn't take away from the fun of driving them. The only newer M car that I really enjoy is the M2 comp. It's a much more analog feeling car. I'd love to take one around a track one day.