My Party is level 6 and I am in the Moonrise Tower Area.
I've been bouncing around to the different companions and trying to get a better feel for what is strong. My impressions so far:
Best to Worst
1. Fighter, Battle Master: She can attack like 6 times in a round, if you blow some cool downs. She just straight up solo's the biggest bad on the field, or wipes out a horde.
2. Barbarian, Berserker: Great mobility with Jumps, good damage & damage resistance with Frenzy. Almost on the Battle Master's level, just can't attack quite as many times.
3. Druid, Moon: The shape shifting is super strong. Great damage and survivability.
4. Warlock, Old One: Decent, consist damage with Mind Blast. Decent Utility and crowd control. The ability to fling enemies around and knock them off ledges with Mind Blast is pretty useful.
5. Wizard: Only used the Gale variant. Probably has the highest ceiling in terms of power, but many of the abilities are also confusing and hard to use. It is going to take some time and practice to use at the full potential.
6. Cleric: Only used the Shadowheart variant. Seems ok, but the fact that you have to long rest to cast your heals is counter intuitive, because you have to long rest to heal anyways.
7. Rogue, Thief: I don't get it. I must be doing something wrong, because the Rogue feels so weak in fights compared to everyone else. Sure, you have incredible mobility, but if all that adds up to one 15 damage "sneak attack" well, big deal... He is basically my rez bitch, that goes around lifting party members that have fallen.
Admittedly, this game is deep and sometimes I feel like I am not using some of the classes fully/correctly. There is a learning curve here.
Still need to try Monk, Paladin, Bard, Ranger, & Sorcerer.