Try them all out. I'll bet you pick the RS5. No point getting a M3 now, IMO.
Then go drive a C63 with LSD and P31!
(j/k)
I loved my E92 M3 and I loved it on the track. That was generally the only time I really loved it (or when ripping it on the freeway with sport mode on). My 335i pulled harder down low in the city and the ultra conservative interior of the M3 coupled with those annoying seats really bothered me for such a nice car. Hell, a E36 M3 with the Vadars had a nicer interior relatively speaking. I've realised that except for the S65 (which I love and will one day swap into a Z4MC), I prefer the E46 to the E92 M3.
Classier this, destroys competitors that (complete horseshit, go look on Fastest Laps), all fanboi self-justifications. Drive the one you want to drive. At the end of the day, a 2/10th of a second difference set by professionals on tracks will not transalate into your doing the same (as someone else said).