The supra is a nice looking car. The M3 is awesome. It really is German Engineering at it's best. It's conservative, well balanced... and a whole lot more money than the MSP.
As a matter of fact.... My family (more specifically my dad) has had bimmers in the domain for a long time. When I got my 99 protege, I noticed how much it resembled my pops '85 318i. 'cept it was 20k cheaper! That is what the protege is! It's the poorman's BMW 3 series. The MSP is the poorman's BMW M3. The only thing is, is that our cars won't last as long as a bimmer. That '85 318i lasted 11 years. The odometer stopped working at 300k MILES about 7-8 years in and the only major work that was done was a new clutch somewhere around 400k miles (really don't know, but we estimated that that car had close to 500k when it finally died). That is why the parts are more expensive. They actually work properly with the car.
This is also why you find so many MSP owners like the Bimmer. They wanted the Bimmer in the first place, but couldn't afford it. So they got the next best thing (even as I did

)
(yes I know that there are subtle differences between the two cars, headlights look different, interior is fancier, etc, so don't flame over minute details...lol)
If you want a million-gazillion-quatrilion-yabba-dabba-doo-zillion hp, listen to the guys and get the TT Supra. If you want to save money to buy a house or something down the line... stay with the MSP. If you want an elegant car, with power when you need it, absolutely 100% get the M3. It is more than just the 330horses under the hood. Those horses won't pop the block by turning the power up a bit, nor will they let you down two months after the warranty ends. Econo cars are known to do such things, because they are built cheaper.