Both are obviously amazing Pokemon in a playthrough, but if we were to decide by what starter you pick, this is how it will turn out...
If you pick Fuecoco: 100% use Gallade, since Skeledirge and Ceruledge share the exact same typing.
If you pick Quaxly: Ceruldege is clearly the better option, not only does Gallade share the fighting type with Quaquaval, but Ceruldege's fire-ghost typing makes it and Quaquaval synergise very well together, as Quaquaval helps with Ceruledge's dark, rock and ground weaknesses, while Ceruledge helps Quaquaval with its Grass and Psychic weaknesses. Gallade and Quaquaval can't support each other by countering their weaknesses so they are nowhere as good as Ceruledge and Quaquaval.
If you pick Sprigatito: This is much closer but i'm giving the edge to Ceruledge because out of Meowscarada's 7 weaknesses, Ceruledge is super effective or resistant to 6 of them which is extremely good synergy, Ceruledge helps by countering the 4x bug weakness as well as the ice weakness, and then is immune to fighting and fire thanks to flash fire, and continues to resist opposing fairy and poison types, though Gallade can atleast counter Meowscarada's ice, fighting and poison weaknesses, so Gallade can actually do better offensively but Ceruledge is WAY much better defensively as it can be good defensively to all but one of Meowscarada's weaknesses.
But if we are talking about the species alone, then Gallade is better, because Gallade has access to extremely good moves much earlier, thanks to having access to the move reminder everywhere you go, Gallade can immediately take advantage to its excellent sharpness ability with Sacred Sword, a new move it learns at only level 1, so with the move reminder, you can teach Gallade that move as soon as you get the chance, Gallade also is an extremely versatile Pokemon, learning so many different moves that he can also take advantage of with sharpness, at level 1, you can also immediately teach him Leaf Blade, Aqua Cutter and Night Slash, 3 great moves that get boosted from sharpness, and by TM, Gallade can learn Shadow claw and X-Scissor for sharpness boosts. As for Ceruledge, until it gets Bitter Blade, the only physical fire move it can learn by level up is flame charge which isn't that strong.
So if you dont care about the starter choice, then Gallade is better.
