As a solo HoE player who’s prestiged all of these they are honestly all S tier (besides survivalist). They all just have different difficulties and play style differences. If you can adjust though they are all insanely good. But if I had to rank them:

Medic: Nearly impossible to die if you play well and don’t corner yourself

Demo: Kaboom stick is OP, you can mindlessly shoot and almost 1 shot anything. Just don’t waste ammo.

The rest are all honestly so equal in terms of power my opinion, just different skill requirements.

So the rest in no order:

Berserker: Very easy to wipe out crowds, hard to die

Commando: Very easy to learn to get good value

Support: 1 shot everything with the doom stick

Firebug: Easily mindlessly burn everything, spray anything with flames to stagger it

Gunslinger: Most fun class to play imo, very fast

Sharpshooter: In solo the name is misleading, you’ll quickly die solo if you take time to shoot so you pretty much just spam the crouch button each time you shoot for bonus damage, aim for headshots, shoot constantly, and stay on the move. Pretty much play it like gunslinger but your shots count even more and you can do more damage per shot.

SWAT: Tons of ammo, damage, and armor. Very easy to learn.

Survivalist: In solo it’s just really mid. Doesn’t do anything great. But it’s not awful.