It probably varies from guild to guild, and from time to time. For my guild it seems to be dps, we’re lacking in wizards particularly. But it can fluctuate. By the last week of kunark we had a night with zero shamans. But the first night of Velious we had 7. So needless to say it’s been interesting trying to parse class needs. I just know we’re in a very healthy position with tanks, healers, and utility. But I’m sure other guild leaders and raid leaders would likely have had entirely different experiences.
I don't have much interest in druid. I may grind a rogue, but rogues and wizards are hard to find groups past 50. What about Rangers?
You ask for underplayed class but don't want to play them, that's why they're underplayed. Play what class you actually want and don't try to chase the meta. Except don't play a rogue in classic, ever, on any server.
Rogues in classic are inexcusably bad. In that there is no excuse for it to not have been addressed when TLPs are the bread and butter keeping the lights on at DPG
Probably midrange on rangers, most guilds have at least ~2-3 high attendance from what I know. They get really trendy in SoL/PoP too because pew pew pew. Other least played option, after Rogue I might say Paladin.
Most needed and least played are very contradictory. Most needed are Bard and Cleric, by a lot. Cleric is the most played class, bard is probably in the top half. Least played are Rogue, Ranger, and Paladin. Why? Because they're not needed and barely useful.
My advice, not that than others here: Always play the class you enjoy the most. Let your guild recruit the classes they need. That said, clerics are always highly wanted for groups and raids and almost every group wants a bard. Rogues/rangers/paladins/sk's seem to be on the lower level of classes being played.