I personally couldn't decide, so I voted randomly! I ended up choosing the triplets. Here's why I couldn't decide...
While Burgh has the levels, the triplets have more pokemon (I'm presuming each one has a lillipup, so 6 pokemon in total) I think it really comes down to which pokemon each one sends out first. If the type matchup is in favor of the triplets (say whirlipede vs pansear) I could easily seeing them pulling through. If Burgh decides to switch to say, dwebble to use rocks, and pansear used work-up, it may be faster and be able to use incinerate. Or, save pansear to take care of leavanny and just use panpour. The lillipups can be used to switch into when the triplets need to heal, and so could panpour as it has a type disadvantage. Although the lillipups could be a small force to reckon with.
But, Burgh does have the level advantage, and with the right start-up, he could dominate the triplets, especially if he's able to dispose of pansear.
I just think each gym leader(s) could potentially win it.
As for favorite? Probably Chili, although Cilan is cool too. I like Chili's personality/hair a lot. My favorite monkey is probably pansear because it's the cutest/I like it's pose the best. As for their evolutions, I like Simisage as it has a cool fro/looks the best.