what's the best catback exhaust as far as fitment is concern?
 

by fitment i meant no low hanging muffler (at least not too low).

The Nameless axle back on my 2013 FR-S doesn't hang down low.

humfrz

Main reason one buys catback usually is better sound. I guess that should be primary criteria over all the other parameters (except maybe quality, as i doubt many will find acceptable for welds to crack & rust through in year after purchase/install).
Fitment? In lot of cases issues can be fixed with retightening/other hungers/hammering/etc :D

Tomei 80r

lol all of them, probably even most ebay ones. I can't imagine it'd cost much to have a muffler shop fix it. You should worry about the sound, and for that no one can help you. Only you know what sounds good to you

i have no direct experience with this, but i have seen people have difficulty getting the Perrin catbacks to sit properly

In terms of low hanging catbacks I would avoid the Megan single exit, it's known to hang very low relative to others.

The Invidia R400 hangs a bit lower than most catbacks.

Also some catbacks have bends that make getting a floorjack under the diff more difficult. Just something to look out for.