1st off, i wouldn't let literally a couple of negative, horror-story type posts unduly influence you. human nature being what it is, most ppl don't post anything when everything is running smoothly, and likewise adopt a 'the sky is falling' attitude when something breaks down.
2nd, i'd do some online reading. Autoweek conculded its long-term wrapup of the MS3 and after ~25k miles, there were only a couple of minor quibbles w/ the car. look up C&D, Edmund's and others.
and after you've read up on it, test drive both cars. you did the right thing by asking Qs on an MS3 board, ppl will tell you their 1st hand experience. mine, for example, is this: car is coming up on 2 yrs anniversary, never a CEL, doesn't burn a drop of oil, and it's a pleasure to drive daily. my biggest headache is identifying/fixing an annoying rattle from under the passenger seat, where the subwoofer is. i'd call that a good deal, reliability-wise.
IMHO it's a no-brainer: 200 hp vs 263. that alone would seal the case for me. (yippy)