>>714096639Soldier: generic cover shooter.
Infiltrator: stealth archer, play it if you like headshotting things.
Vanguard: prime things with companions, lock-on charge them for an explosion, and then shotgun them in the face. The most fun class if you like getting into melee range.
Sentinel and adept are similar classes. Both hide from cover, prime enemies with one ability, and then aoe combo them with the second ability. Adept is more fun to play because it's stronger, but more fragile.
Engineer: hack mech enemies or overload enemy weapons. Maybe the most boring class.
Conclusion: first choice Vanguard, second Adept.