the barb is very easy to play in group fights and soloing no matter what feats you use, but i recommend starting as zerker just to know a bit how things work, then try the reaver
the conq, i havent played it yet, but since revamp, and at lvl80, at least is very good to tank in groups, solo or even help dps on group if necessary
"not great tanks as well"??? - guards have very high health and can maintain aggro for a very long time, specially using sword-shield with juggernaut + general, that is very useful when dpsers are sin and an hoc for example (lots of dps and aggro to control)
"they not do DPS but apparently"??? - on soloing pve with polearm and tempest build i can kill at least 4-5 mobs in khitai (lvl80+) using heavy armor
the biggest problem i had with the guard was only lvling until lvl 80, that compared to other class like barbarian and bearshaman, is much slower (its not a problem actually, just time to kill mobs is longer for guards at low levels)