Look for an '85 GT 5 speed. +'s = roller motor, 4V carb, no EFI easy bolt ons. -'s = 7.5 rear, dual into single and back to dual exhaust. Other than the third brake light, looks just like an '86. In addition, it will be worth more down the road. Last of the carbed 5.0s. I have a black '85 GT with 40,000 original miles and a Charcoal '86 GT w/ T tops with 58,000 original miles.
It depends on what you like messing with---V8s or turbo 4s. SVOs come with lots more done to them from the factory in the way of 5 lugs and 4-wheel disc brakes, but there's lots of SVO specific parts that you'll pay through the nose for.
If you're looking at something "cheap" to buildup I'd go for the GT. If you want something a little different in looks/power and would like the challenge of something not so "mainstream" then I'd say go for the SVO.