If you have forbidden magic (thaumcraft add on), there's an enchantment that exponentially increases the amount of XP you can get. Its called Educational, and though it may be hard to get on a weapon (Easiest way is through the Osmotic Enchanter from Thaumic Tinkerer), a Sword of the Zephyr with Educational V produces so much experience that I don't know what to do with it. Killing a single blaze gets you 9 levels, and it is so efficient that I didn't bother with an XP grinder. I just turn on a mob spawner, whack a dozen or so enemies with a few swings and then I'm well above 30.
I haven't experimented with dynamism tablets or autonomous activators, but if they retain the enchantments on weapons, then a single educational V sword will cause you to literally drown in experience.