M3 is the most fun and obviously the fastest, but is the least competitive unfortunately. TTB is full of S2000's with wings and e36 racecars, a pretty much bone stock E92 would get raped. You start with 14 point penalty in the M3, leaving only like 5 for mods, so really the M3 is a TTA car.
For a car that won't be purely track the M3 is more enjoyable because it is so much faster and has an awesome engine note (with an exhaust). If TT is that important to you then I'd pick none of the above, and if it isn't I'd pick M3.