Mando is easily the strongest character in Alien Armageddon. Not only all of his weapons are excellent and simple to use, the shotgun being, perhaps, the most ridiculous one, with one cheap upgrade it turns into a shell fed grenade launcher. But he also has the strongest H-item in the game, which charges from kills, which is unique to Mando, and doesn’t take damage from the enemy attacks, like Wes’ one does. And on top of that, Mando comes packed with additional mobility thanks to his jetpack, which is very convenient.
Bombshell, in my opinion, might be the weakest one due to the lack of nuke in her arsenal; she’s the only character that doesn’t have access to it. What hurts her even more is that her slot 6 weapon – the turrets are a sustained damage thing. So when you need to nuke a room or quickly clear a group of tougher enemies, which happens often in the mod, your only option is using her rocket launcher, which is nothing special even when fully upgraded. However, it doesn’t mean that she’s weak in general, she can blast through the game just fine, it’ll just be less convenient to play her in comparison to the other characters. And you probably won’t even notice it in the new episodes, because they are generally very easy, only episode 2 – space gladiators provides some challenge, but it might become much more apparent in attrition mode, which isn’t shy of killing you.