I swept through the game with my Empoleon, Roserade, Luxray, and Rapidash.
Around Crasher Wake I ditched Rapidash, it was level 51. Then I took on the Elite Four with Empoleon, Roserade, and Luxray, all in their late 40s, and won
Now it's just Empoleon and Roserade I guess, they're the only ones I really train every now and then. Empoleon is in her 90s, Roserade in her 80s, Luxray in her 60s, and Rapidash still in her 50s.
But I use a competitive team (thorough sweeping) for the Battle Tower, and they are: Floatzel, Leafeon, Lucario, Gardevoir, Houndoom, Granbull.