If you can, just make an Enderman farm in the End. You know, the one with pistons that just drop them to their deaths, built far from the main landmass for spawn efficiency. That's what I've been using for infinite iron, gold and diamonds. And anything else that you can transmute with those materials. Mine even converts to an XP farm, but I hardly use it as I have a tier 5 blaze spawner that gets me 30 levels in 30 seconds.