What an odd question...
Dont think you can call either tacky tbh."
I 100% agree with that, neither are "tacky" cars but if I had to choose I would say the Mazda on the reasoning you're probably 100 times more likely to find some RX-7 with some tacky neons and some lurid over-sized body kit which doesn't fit properly than your likely to find a Sapphire Cosworth with any tacky body modifications.
If your asking which one looks better as standard.. personally I think the RX-7 looks an amazing car, probably one of the best car designs.