I just realized how old this thread is.
Well Ultimate Kuuga still reigns supreme, over Double, Decade and at this point, OOO. Kuuga can use all the secondary ability of Pegasus, Titan and Dragon in Ultimate Form. So yeah, he can't slow down time, but he can sure run and jump fast, and as Decade showed, even regular Pegasus can predict the location of a Clocked up Rider, plus he has immense durability from Titan.
I feel bad for Hibiki, no one thinks he is the strongest....