1. Atlanta United
The rivalry with Atlanta United is a really unique one, because it started out as one of the most forced "derbies" in all of MLS. There's not much rivalry between the cities of Orlando and Atlanta and no previous soccer history between the two.
But after five years of battles, Atlanta and Orlando are sneakily two of the biggest rivals in the league, at least one of the most underrated rivals in the league. This derby has gotten legitimately nasty, and I mean that in the best possible way.
I was fortunate enough to attend the US Open Cup semi-final between the two in 2019, and my god what an atmosphere. Despite only about 35% of the stadium full, this was the nastiest I've ever heard Exploria and it was awesome. The amount of vitriol directed at Brad Guzan and especially Justin Meram was insane and the energy from the Wall was unmatched.
Moments like that are becoming more common between these two and the rivalry only gets better as both clubs look to push into the elite tier of MLS. I still pray that these two meet in a playoff semifinal someday soon because that would be the best non-championship game in both club's history.