Make a character as much of an opposite of who you are going to have as your main character. You jumpy little Light types, you get to be lumbering Heavy tanks. Stealthy Operatives, you are now noisy, trigger-happy Soldiers. And so on. Think about your anticipated playstyle. Then turn it around; figure out how you could play exactly not like that. However, you still want this to be a successful character. Select some key Abilities and weapons accordingly to focus your character's role. Or, be creative and unusual (maybe stick your Heavy with an SMG and a Pistol? :blink: ). See what you come up with. Perhaps he'll turn out to be a character you'll play down the line, since you do have 10 character slots available. (Note that since you can change factions with the same character, that will not be discussed here.)
Main: Medium Engineer/Operative who focuses on buffing weapons, fast-paced close-quarters combat with his shotgun and silenced SMG, and securing Command Posts and secondary objectives for my team.
Opposite: probably a Heavy Soldier with a grenade launcher and an assault rifle. He'd be a primary objective hog, always guarding what needs to be guarded, or blowing up what needs to be blown up. He wouldn't care about what the other players are doing so long as he is able to always stay on track with the primary objective.
Your turn.