When it comes to online play, I'd say it's a little more complex, as it depends on a lot of things, such as what Pokémon you have access to, what their abilities are, what IVs they happen to have, and so forth (though, you probably know about them already, haha). From all those Pokémon that you had listed above, I'd say Hydregion would make a pretty great member of your competitive team. It may be weak to a variety of types, being a combination of dark and dragon and all, but its offensive stats are pretty large, and with them, it would wind up to be a great attacker.
If your Hydregion's got Modest nature, then moves I would personally recommend for it are Draco Meteor, Dark Pulse, Surf, and either Flamethrower or Fire Blast. If it's Adamant or anything else, then you'd like be better off with Outrage, Crunch, U-Turn, and perhaps Earthquake. Couple of other choices would be Head Smash and Thunder Wave (latter's for slowing opponents down, so that you could gain an upper-hand).
I've tried both of these sets, and they're great overall!