I use mob heads because I get loads of them from my mob farm (or at least I did at one point) and there is no crafting at all involved, just put them down.Crystal clusters were the easiest to do and I already had an overabundance of shards. Meanwhile, I don't have mob heads stored and they can't be arranged vertically, and tallow candles require a two-step process to make. In fact, I'm wondering why other people don't use crystal clusters as much.