JackOfAllTirades
Explorer
Oh, and Evard's Black Tentacles is surprisingly effective too. Especially when someone runs into it on their turn for some reason--if they've already used their action to attack or something, then failing the Dex save and getting snared is an automatic 6d6 points of damage (because 3d6 happens when you first get caught, and 3d6 happens at the start of every turn you're ensnared). That makes it almost as good as Fireball at AoE damage. I ran a whole squad of 8 umber hulks into Evard's Black Tentacles (in a chokepoint) over the course of 2-3 rounds and it was really painful and demoralizing for them.
EBT was pretty much always a game-changing spell since its first appearance, so I'm not sure who considers it "surprising" any more, let alone underrated. I think at this point everyone knows how good it is, and unlike some other spells, it didn't get an unexpected power-up when converted to 5E.