I would stay away from first year E90/92/93 models...I also heard that 2008-2009 M models had rod bearing issues...I cannot confirm this because I did not read up on it since I'm not in the market, but just "hear-say"...
How many KM does the M have that you got a quote for? Are you looking at manual or DCT?
E46 330i (Sold)
E90 328i (Sold)
E90 325i (Sold)
E90 328i Xdrive (Current)