As a general rule, the three gasoline brands you will most often encounter on that route will be BP, Shell, and Exxon/Mobil. RaceTrac stations are very common in the Southeast as well, I think they self-brand their gasoline. AFAIK, all of the toll roads in Florida are serviced by Shell at the moment, but you won't be on that many toll roads if you are only heading to WDW.
Here locally, Phillips runs good incentives on their gas cards (UGas uses Phillips), but IME you won't find many Phillips dealers in the Southeast. Note that QuikTrip isn't all that common along that route, either, except in the Atlanta area.
Note that if you take the Alabama route you may find a different mix.
FWIW, I *strongly* recommend the Alabama route if your timing would otherwise send you through Monteagle on 24 in the wee hours or in predicted bad weather; that is a killer road for truck accidents when conditions are sub-optimal. (I was hit once by an out-of-control semi -- that's NOT an experience that I ever want to repeat.) The Chattanooga route *is* shorter, but the potential for danger through Monteagle has to be taken into account. It's perfectly safe in the sunshine, but gets very nasty fog overnight, and trucks can have serious trouble on the grades at anytime if it is wet.