I voted Burgh because it's a great challenge.
For the triplets I think it's too easy to beat them. You receive THE pokemon who has an advantage. Also, If they are really gym champion's, they don't need to take the better type in front of us. They should be strong enough to fight us.
Plus, Burgh have some good pokemon. It's the third champion and his pokemon have a little level to beat the 3...
I think it would be more interesting if we have to fight against the triplets. Begining with the type we have an advantage front. After go in front of the middle type. (we have no advantage and no handicap). And after, finish by the type we have a handicap. They respresent a real challenge in this case.