## Neither *Bless* is "more potent" ##

They both allow the affected person to add 1d4 to an attack roll or saving throw - this is the same potency. The player does not know ahead of time the result of either roll so there is no difference between the effect - add 1d4.

Therefore the DM decides.

## For most practical purposes, it doesn't matter ##

If a character is under the effects of 2 (or more) *Bless* spells, then they can choose to use one and that one no longer affects them. They can then use another on a subsequent roll (and so on).

*Bless* has a duration of 1 minute which is plenty to cover any single combat so deciding which *Bless* was used and which wasn't has little practical effect apart from knowing which caster has to keeep concentarting and which doesn't.