Veers, Piett, Dark. That is the core and will beat the most teams. Range is the optimal 4th, and then gideon if you need to outrun teams you cant outrun with piett (that is implying you have like 170 speed on piett and/or gideon, if you dont, work on your mods.)
If you dont need the extra speed from gideon, starck is fine, he will help you with the tm train, and especially in pve his tm reduction passive is very valuable
and if you cant outrun DR even with a super fast gideon, shore trooper is the solution to that particular problem
the other troopers are fine as well mostly, with dark and range trooper in the team, you should never have problems keeping the train going, either by killing a target, or just with all the assists from range