I play elementalist a lot, which are absolutely amazing for the boss wave. With wall of fire they can hold the door really well doing a lot of damage and fearing enemies that come inside. Along with firestorm, you can absolutely decimate the normal mobs giving space for your team mates to deal with the boss. Along with this, you have barrier on a very short cooldown which is a hard counter for the demon commander. Honestly, elementalist is amazing and I think it's the best control class for the boss level.
It's always good to have one person that has good control skills and/or survivability that can deal with the normal mobs. Arcane warriors, elementalists, necromancers, legionaires, templars are good for this. This gives room for 3 people to kill the boss. A good legionaire should be able to do this easily. Templars and necromancers might have a bit more of a problem. Never really played necro but i know they have blizzard. But, this is how I do it because I usually play in a coordinated team.
FOR PUBS, I feel like 1 good tank should distract the boss while 2-3 people kill normal enemies. This is usually what happens.
If you play keeper just make sure to barrier your team mates, that's the most important thing you can do as a keeper.
Don't group up unless you're receiving a barrier.
Venatori is really straight forward. Not much strategy needed for this. Your biggest problem are the juggernauts. Just don't be dumb and get hit by them. Venatori is mostly melee so kite them and have good CC, and it's a walk.
Red templars, kill the captain knights when you spot them. The boss is pretty straight forward. All you have to do is kite him. Once he's on his 3rd stage just keep an eye on him incase he jumps on you or uses his ranged skill. Usually on this boss a lot of the time you kill majority of the enemies before you actually kill him, likewise with the demon commander.
As long as you have one good tank, you should be able to succeed. A good tank can do so much.
When there end up being a lot of ranged enemies (wraiths, archers), it's good to quickly wipe them out. The tank can usually do this but sometimes a 2nd person might need to help out. Archers are the best for this.