I was in the same position and went with the M3, I picked up an 05 ZCP. The E46 M3 is a special car (its my 2nd one) and you wont have a chance to own one for long. It thinks its a race car, I love it
E92's are nice, but common, and you'll be able to pick them up for years to come.
Do a search as this topic has been beaten to death.
Go drive them, they're different cars built for a different purpose. The M3 can get old quick if you're not up for it...
Really cant go wrong with either one... I would be happy to own either one.
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Current: 17 OG M2 / R8 Performance
Past Performance Cars: 01 M3, 05 M3, 06 M5, 08 M6, 08 M3, 11 M3, 13 M3, 15 M3, 911 C4S, 911 GTS, 17 M2,R8 V8, R8 RWS