Try Rogues. Player's naturally get into the idea of planning heists, robbery and other such nefarious activity alarmingly easily. My 2E game like this has at its peak 12 players for a few sessions which was far too many. A normal sized group or a smaller one works better and is amazing/Yeah, I can't really think of any that I would want to play either.
They all sound pretty cool in theory. Druid is my least played class, and yet a party playing as a circle of Druids sounds awesome.
The hardest part with single class campaigns is getting everyone to agree on the character class in the first place.
We had a 1e campaign go in the other direction - everyone was playing a fighter or ranger, either single classed or with a bit of multiclassing to wizard, cleric, or thief. We were mercenaries, so it was irregular military-heavy in its approach. And it worked just fine.The closest I ever had was in 1ed. It was a party with all mages of multiclassed wizard and only one dwarven fighter... That group was a terror to behold as every single fight it was: Fire ball, lightning bolts, Ice Storm, Cone of cold, Magic missile and the Dwarven fighter waiting to see if something had survived... That dwarven fighter had boots of striding and springing and would often be running in the dungeon to bring enemies to the other players. Once the alert was given... well you know the drill.
In 5E all Bard party needn't be a band or troupe of entertainers either. They could be explorers, archeologists and all sorts of things. Such a party could handle almost any problem though skill overlap might be an issue.I would probably play any single class party if presented with that.
We did have a joke about an all bard party that some of us started talking about actually doing.