Generally observations I've made...

2 Handed weapons typically like to go on rampages against enemies. I always get more and longer combos with the 2 handers.

Certain weapons themselves are prone to comboing-for instance, I'd never seen Lady Ashe really do meaningful combos until she just got her Diamond Sword-now she whips out 5 hit combos like it's no big thing, and all I can say is "...alright then!"

The poles typically seem to hit for 2-3 hits reliably, although I've seen Vaan go sick house psycho on something and pull off chained together six hitters.