A turbo MKIII Supra will run 15.2 stock while a MKII MR2 will get around 14.5
But the MR2 "plus points" stops right there.
Theres a huge different between an Inline 6 and a hard to reach centered 4 banger.
Just changing the exhaust and intake filter on the Supra will give you a huge benefit! (Low 14's)
As far as the rest goes, you'll have way more fun with a bigger car, and get Targa!
So my vote goes for the Supra, I6T torque, big and powerfull yet very agile and beautiful for a 10 year old car.
If you're serious about getting one, I could still consider selling mine.