Hm, for the Ultras I can't say since I haven't seen many honestly, neither have I seen that many sentais. But for Riders, Kuuga wins it for me hands down. Agito's song was awesome, but geez was the opening boring beyond the starting part.
Ryuki's 2nd for me. I really loved what they did with Ryuki's posing part when the sparks started coming from around the mirrors. The end of the opening was awesome too, Ryuki walking down the road with the Dragon following him.
Faiz and Fourze as 3rd, I can't pick which.