value, it's a toss up again, but the BMW will probably hold its value better than the TTZ. They're both good cars, just depends on what you need. If you need a car to drive long distances on the highway the Z is probably better, but if you need to zip around town and occassionally carry a couple passengers then the M3 is probably a better choice.
"It's been my experience that straight-line acceleration is probably the first aspect of automotive performance that any intelligent driver gets bored with." - Peter Gregg