Of those you listed, Gallade would be my pick, as my Gallade has done some serious damage with swords dance + close combatting entire teams to death. But if you wanted type coverage, I would do the prequest to get a beldum and train it to Metagross, as that gives you Psychic, Fighting, and Steel just on level-up moves. Aside from both of those, maximum bulk + type coverage is achieved by Scrafty, as you could either go Bulk Up or Dragon Dance (event only, you'd need to reset for the egg move) and end up destroying teams with Crunch / Hi Jump Kick / elemental punches. Personally, I don't like Sylveon as much as the others, mostly because Glaceon is an insanely hard hitter (especially with frost breath) and I feel like it would be better for you to go with diverse type coverage over a hyper voice fairy type.