Archers have the longest range, but can hit only one enemy at a time.
Mages can hit at mid-range, but their attacks are AOE. Better for enemies you've grouped together.
Knight can take an extra hit and attack at close range.
It's definitely hard to get any one particular build going when things get chaotic, but I like having to adapt on the fly to what survives. Glad you also had some fun even if it was a bit vague~!