FD's omni-battle thing. Man. I'd put my bets on Archer, followed by Nanoha. The Blink thing I didn't remember, but if he's just immune to spells Archer would fillet the poor bastard, and everything else is just... from lower power realities, so to speak. Archer's actually a bit broken in an arbitrary sense -- dude's primary shtick is to be able to recreate magical artifacts, and then potentially supercharge them and make them explode. He's largely limited only by the arsenal you decide to let him play with, and for the period before reality notices they're there, the stuff he makes is as real and physical as the originals. His secondary shtick is he's basically a self-made Elder God of Swords, at least in a limited physical area. Reality marbles are wonderful, heh. E: Wait, wait. It might depend on the Archer. The one before CG-Shirou... might actually have been worse, I'unno.
As for Nanoha, magery's all well and good in the case of the rest of them, but she's something a little bit different. Crazy witch is a human sized mecha, with most of what that entails, with a side course of magical fuckery. Gandalf can You Shall Not Pass all he wants, I don't think it's going to help much against a beam of energy capable of scuttling an interplanetary warship from over the horizon.
As for the rest... yeah, those two are in the category that can casually destroy mountains and/or countries/(in archer's case, potentially planets, given the right kit. Iirc, there's anti-planet level artifacts out there. Dude could also just conjure up a sun crusher or whatever.), if they particularly feel like it. The rest of the lot are a bit more... subtle, from what I remember.