So I've been thinking about Serperior and common situations I found myself in when it battled, and I've come to the conclusion that I think Hidden Power Fire is the superior choice over Hidden Power Ice. No, not because of Twister (lol), but because of one thing, and one thing only: Genesect. Unlike, say, Dragonite or Lati@s, who can easily be trapped by Chandelure if need be, Genesect provides a serious dilemma when you're facing it with a Serperior. You could sacrifice something to Dnite or Lati@s and then easily revenge kill with Chandelure, but in Genesect's case it can and probably will U-turn, making it very difficult to pin down with Chandelure, as you often have to sacrifice something like Garchomp to Ice Beam in order to prevent Genesect from slipping out of Chandelure's grasp with U-turn and right into the arms of Tyranitar.
With Hidden Power Fire you can now hit Genesect as it attempts to sponge Leaf Storm, allowing Serperior to start throwing them out more freely later on in the match. Glare seems like an ideal move for Serperior the more I think about it since a paralyzed Genesect is far easier to catch with Chandelure. Leech Seed is very important as well, though, as Serperior is easy to wear down if it's the team's primary Water-resist. Leftovers seems better in most situations than Life Orb (unless it's like on hyper offense with screens or something), as Serperior wants to see as many turns as possible to increase the likelihood of getting enough boosts for a sweep, something that Life Orb actively works against.