TT is quicker spooling, instant power. Single means a compromise A/R turbine side because it feeds off 8 cylinders worth of exhaust so, it has to be big and that means generally requiring more effort to turn and thus more delay. There are ways around this, like twin scroll but, those are more complex solutions OEMs typically use. The pipe runs on the hot side of a single are more complex when fitted to a V engine and that can contribute to lag and packaging issues.
Downside of TT is packaging two turbos, their oil and drain lines and coolant hoses, two turbos to go wrong instead of one and underhood heat.
TT is definitely preferable on a street car, in this application.
Turbos are hardcore, man. It's A LOT of fiddly assembly work, even on expensive systems and generally lots of niggly maintenance hassles down the road a few years.
I built my own TT kit out of junkyard parts years ago on my 88 5.0. Holy **** did that make power, until it squeezed out its head gaskets. It was a blast. Then, I went with a centri blower, which was much easier to tune and lower maintenance.
I'd kinda think of it this way, if you like your car to wow with hood up at car shows or on jackstands, go turbo. If you want to drive it everyday, go SC.
2014 Premium GT, SGM, Brembo, Auto, Tech, Comfort, etc. GT500s, Steeda UCA, VMP auto N/A tune. 100 shot nitrous on BBR tune. Best e/t 11.38 at 120.85
2012 Premium GT, Candy Red, Brembo package, 3.73, MT82, Comfort, Tech, et al. Procal tune, Roush UCA, UMI poly LCA, GT500s, Steeda red bracket, Hoosier 28x10x16 bias drags. Best e/t 11.91 at 115.23 RIP