BA = battle arena, 120 dc, 7 units max
TA = ticket arena, 120 dc, 5 units max
GA = guild arena, 200 dc, 10 units max
Compare with colo, other above have more dc and allow you to get better units to form a team. In short, it is all about dc
Colo = 100 dc, 5 units max
Remember, in general, the higher dc of a units will always has better hp or/and attack.
For example: Reinchard with dc 30, super meaty 6*; Delfina, highest dmg output among all 6* quad hit unit
Of course, I just use 6* as example, but some 5* or 4* can be good too if you low on budget.