Well, both are great games. Super GT has a wide variety of cars and tracks and some awesome music. A SGT cab also offers the chance to run other Model 3 racers such as Daytona 2, Sega Rally 2, Dirt Devils, Emergency Call Ambulance, and Lemans 24.
Outrun 2 is an excellent choice, as well. While the Chihiro platform doesn't give you much diversity (the only other racer is WMMT2), you can plug a Naomi 2 directly in and run the Initial D series or maybe Crazy Taxi. The major bummer with this cab is the GDROM setup, which is more problematic than the Model 3 stuff.
If you are just comparing the games head-to-head, OR2 is the clear winner. However, SGT is an incredible racer, too, and the easy conversion to other stellar racers is something to consider.
Really, either way, you win.
