Sacrosanct
Legend
You weren't supposed to play 1st edition Assassin, it was presented as an NPC only class (Like Death cleric and Blackguard in 5e) hence it's always-evil alignment restriction in a game where evil PCs where discouraged.
Having said that, I did see them!
It was not presented that way in the PHB. It was presented as an actual playable class (specifically subclass of thief). You're thinking of the classes in the Dragon magazine, which many were presented as NPCs (like the anti-paladin). But the assassin was very much a core class in 1e.
To the OP, I've seen them all played fairly often (except warlord for obvious reasons already given). I've seen the fighter, druid, wizard, and bard probably the most common in 5e, but all of them, including the monk, have made appearances more often than just really rare.