Pathfinder's dispel magic allows for someone to attempt to dispel one spell on someone. The process for selecting which spell is dispelled is specified.
Targeted Dispel: One object, creature, or spell is the target of the dispel magic spell. You make one dispel check (1d20 + your caster level) and compare that to the spell with highest caster level (DC = 11 + the spell's caster level). If successful, that spell ends. If not, compare the same result to the spell with the next highest caster level. Repeat this process until you have dispelled one spell affecting the target, or you have failed to dispel every spell.
When all spells affecting the target have different caster levels the order for checking spells is clear. However, if two or more spells have the same caster level (a very likely scenario if you have a single spellcaster doing all the casting) then the algorithm becomes ambiguous. If your check is able to dispel one of multiple spells with the same caster level, which spell gets dispelled?
Does the caster choose? Does the target choose? Does the GM choose? Does a spell get selected at random? Do we select spells with higher spell level preferentially? Or is it completely ill-defined and players should ask their GM which ruling will be made at their table?