2" is all that will fit up to the exhaust manifolds, but can be stepped up if needed. 2-1/4" is pretty easy to work with / get to fit and there are alot of muffler options.
The TTI exhaust system is good and has mandrel bends for good flow. The turbo mufflers flow good and are not super loud.
The down side is your labor to install them, unless you have someone else do the install. If doing the TTI, the 2-1/2" system with H-pipe would be my choice. The X-pipe isn't worth the extra money. I put the X-pipe 2-1/2" system on the Convertible and it is fine, but I don't think worth the extra cost. I have the 3" H-Pipe on the Charger and it works great. Have another TTI 2-1/2" H-Pipe for the small block Coronet 500.
With exhaust shops, you need to do some research to see who does good custom work, and what they charge, and when they can do the work.
Most muffler shops don't do mandrel bends, so and tight bends in the pipe will be slightly crushed. Usually the larger diameter the exhaust, the worse the bends are.
The fitment will be to the ability of the employee making the exhaust. Quality of components will be what the shop uses and can vary quite a bit, that is why you need to do the homework and maybe see other customers cars.