Man, people always bring up Quadraxis as their favorite boss from that game (and maybe the series), but I never saw it. Sure, the technical part of it is really cool, but the game had a bad habit of getting in your way, and some elements of the fight aren't well-designed. The 'blinking blue' kneecap weakness should be telegraphed to the player earlier or it should have a better hitbox. The camera in the last phase of the fight isn't reliable for boosting from the spider rails to the top of its head and you have to time against your instincts. The mini-quads summoned later on are more annoying than a serious threat - They sort of appear near the end of this endurance run of a fight and are just there to distract you. The colored troopers in the Omega Pirate fight from Prime 1 are more engaging imo - You hear them coming and they're very direct and swift in their actions.
I'd probably go with Omega Pirate as my favorite fight overall but if we're sticking with just Prime 2, Chykka, although I admit I'm being a bit unfair. I sort of discount the first half of the Chykka fight, which is a boring slog, because the second half is so adrenaline-pumping. The music picks up, the platform you were fighting on splits apart, and Chykka itself is very animated. There are some annoying parts to this fight too like aiming its moving tail and Seeker Missiles sucking in general, but Chykka feels more satisfying to me because the progress feels palpable.
