If you want a coupe, the 1M is a much rarer car if that matters to you. If you need/want a sedan, M3 without a doubt.
Personally a 1M with an S65 swap would be an amazing car. I saw a VO 1M driving down the road last week and it looked good, I was surprised how good it looked actually because I don't really like the regular 1 series.
2011 E90 M3 ZCP - Individual Moonstone/Individual Amarone Extended/Individual Piano Black With Inlay:LINK!!!
1994 Euro E36 M3 Sedan - Daytona Violet/Mulberry:LINK!!!