As a new owner of a used '02 M3 (owned 2 weeks, of which 7 days in the shop so far), and a used '00 NSX (owned 6 months, 1 day in shop, routine maintenance)
ummm... I probably could end the post right now with that statement, but...
I think each car has its own strengths and weaknesses...
I agree with much of what was said above, especially PLZ and lowellhigh
here is my opinion of each car's pro's and con's:
NSX
Pros:
-feels faster, handles better, puts a smile on my face everytime I take turns
-gets looks from everyone
-great feel for the road
-I prefer the NSX shifter to the BMW shifter - feels like shorter shifts
-amazing reliability
-great residual value
Cons:
-2 seater
-I worry about the car more when parking, driving in traffic
-radio could be better - i.e. would be nice if it incorporated new technology like CD-player
M3:
Pros:
-good car, handles turns well, just not quite as well as NSX, puts a smile on my face when I accelerate
-interior, leather, options are superior to NSX - has great "civilized" comforts with lots of cool gadgets and features
-sunroof is better than NSX Targa top
-gets looks from BMW owners
-I think it is one of the best 4 seater sports cars you could buy
Cons:
I think my shop statement above sums up reliability
also, i think acura service is much better than BMW service... less "holier than thou" attitude
I think the best way to sum up my feelings is that I enjoy driving the NSX more on an empty country road and I enjoy driving the BMW more in traffic.
Good luck with your purchase!