you will have to give some more detail bud
but heres a breakdown of the characters and what they did best for me (Always get the "Extra Accesory" upgrade)
Force Commander - Level up the melee and health tree, i tried ranged once and was kind of dissapointed
Tarkus - Level up his Will until his Grenades become energy instead of supply based, they are AMAZING that way (they still have to be equiped though!). and max out his health tree asap so he cannot be killed unless drained of energy from
Tac Adavnce
Cyrus - My boy! Level his Will until he can use equipment without breaking stealth and you can have a feild day with remote detonaters. they are BRUTAL.
Thaddeus - Chapters fury (melee tree) is great since you can just keep jumping on people with the packs but thats really all the use i found for him.
Avitus - Kept him with a missle launcher all game for taking down big targets hes kind of a must later on. i got him his extra accesory then just leveled ranged until it was maxed out, then go to health
Hope that helps a bit!