There is NO QUESTION in my mind.... 914 wins, no contest.
Worst case put a WRX subaru engine in the 914 and that would be a pretty bullet proof car if you dont abuse the transmission. Also, the 914 is one of the coolest looking cars EVER when set up right.....
Any time I see a miata, I feel bad for the person driving it

its just so darn ugly.
The 914 is a beauty.