I had a 2009 M3 DCT Sedan, I now have a 2012 135i MSport DCT. The 135 is faster in town, where most of my driving occurs. Plus, cost of running an M3 exceeds the 135 by quite a bit.
I would NOT trade back for the M3.
2012 135i E82 MSport 6MT Jet Black
Previous BMWs - 2012 135i MSport LMB DCT(sold), 2011 X3 35i MSport VR (sold), 2009 M3 Sedan AW (sold), 2008 535xi MSport AW (sold), 2007 328xiT Barbera (sold), plus 11 others in the 70s & 80s.