I love my E90 M3 but will always have a soft spot for my 07 STI, it's just such a forgiving car and reliable as hell, even at Stage 2. Would have loved to upgrade the turbo on that thing to a GT30 or GT35. But, I wanted to get rid of the boy racer look and all of the attention (ricers and cops).
Plus, the wife is a LOT happier with the M3. Muuuuuch better ride than the STI, she absolutely hated all of the bumps.