I've broken enough tire levers that I'll only use metal levers from now on. When a tire lever breaks on some back road in France just before dark, you might reflect on the few dollars saved on plastic levers. Then you can throw the broken lever into the middle of some vineyard in frustration and hike up to that farmhouse guarded by a crazed drooling dog the size of a water buffalo. Should you survive, you can ask in broken French if they have a tire lever you could borrow. Of course they will, but it'll be sized for their tractor.
Lezyne Alloy Levers are constructed of polished, aerospace-grade aluminum for a high strength-to-weight ratio. They are, in short, the best tire levers we've ever seen. The admittedly high price includes two levers and a neoprene sleeve (so they don't rattle in your tool bag).