My 2 cents...
I had an early '08 135i and I like the 1M. I even had my name on a list before the 1M was official announced.
Everything the 135i lacked (forget power), the M3 had. Better seats, better suspension, better interior materials, more room, etc. Of course you also pay for this. That being said, I went with the M3.
Both are great cars, but they target different groups.
2 LBB DCT
M3 AW DCT SOLD
2008 135i AW 6MT SOLD
MZ3 EB SOLD
1998 Z3 AB SOLD