Whatever you enjoy, you should be able to find a group. Shaman is the way I'd lean if you are really indifferent since almost everyone is running a healer Mercenary. So even "full" groups can often make room for a shaman. And their ability to root rot is currently awesome for solo.
Bard. Bards make every group better regardless of configuration, and are still more rare than most classes. They are fairly unique mechanically and take some practice to run well. Shaman if you want to mix in healing (sometimes primary healing) with your utility and adps. Enchanters are in a good spot right now, very solid dps along with all their support and crowd control abilities. Rogues are in a rough place right now, very good dps, but easily replaced with any other dps class. Narrow class.
In the early eras crowd control is probably second to healing in terms of group desirability, and mana buffs are nice as well. I'd say chanter!
Confession to make: I am a Bard hater! Just the way some people don't like spiders, Bards give me the creeps. That being said, they are a great addition to any group because they make everyone else better. Their healing songs mean less oom moments for healers, their fight songs make MOBs drop faster, their utility for things like mass group invisibility is 'The Trick', the whole group progresses faster in every way. Even as a hater, I ran a Bard up to the mid 60s back in the day just to see what they were about. Darn fine character. Enchanter is nothing short of great too. They can be valuable even when poorly run by just casting Breeze and/or Clarity on the group members that do know their jobs. A really good enchanter can just about accomplish the impossible with charms and mez. Shaman is another really hands on character like an Enchanter. Once again, they are the grease on the wheels that make the train run faster. Rogue, hehe. There have been many complaints from Rogues over the years about in ability to find groups, more so then any other class IMHO. There are a number of problems with Rogues in that in order to use their DPS output, you need a really good tank that can keep aggro. Everybody loves making the kill shot so there seems to be a bit of reluctance and to try a DPS member and disappointment when they don't get it. There was a time when Rogues had incredible utility in that they could sneak through the most dangerous areas to recover your corpse for you. Not so much needed now with equipment staying with you, corpse summoning, et cetera, all but making old Rogue functions obsolete.
