Perhaps i can be of some assistance, having owned both a Supra and two RX-7s.
Ok first off i've owned 2 1993 RX-7 twin turbos. I still own one now.
The Supra is by far the more reliable vehicle between the two. The build quality is a little bit better as well.
The RX-7 on the other hand does not suffer from poor build quality, it's just that the 1993 and up RX-7 was built for one reason only: As a track car. It is not:
1)a daily driver
2)comfortable over extended periods of time (i.e. long road trips, etc)
3)reliable
4)cheap to maintain (huge emphasis on this one

)
5)cheap to work on
That is not to say that i do not love my RX-7, but rather for one to truly enjoy an 1993 and up RX-7 you have to come to terms with the car's inherent shortcomings. The 1993+ RX-7 needs reliability mods like a upgraded aluminum radiator, a aftermarket downpipe to help reduce underhood temps, an aluminum Air Seperator Tank (or eliminate it altogether), a larger intercooler (stock on is laughable small, probably made by Fisher-Price) and all the stock rubber vacuum hoses should be replaced with silicone units.
It all boils down to what you are looking for. If you are looking for a daily driver, don't look for a 1993+ RX-7. If you are looking for a serious, no-frills, uncompromised supercar and are willing to address the downfalls then you might check out a RX-7 Twin Turbo.