I find normal or dark types the best types to be given moves like metronome/thief/assist, since they can't be easily killed (apart from fighting for normal, of course). Snorlax is probably the best to have metronome, since it has good stats, and if it calls up a physical attack on roselia or the nido families it won't be poisoned because of its immunity ability.
I just mention the whole type thing because I once gave the thief TM to a sandshrew/sandslash. I will NEVER do that again, because that automatically prevents me from using thief for the shards on clamperl/relicanth/chinchou. Mightyena is the only pokemon that I let have the thief TM.