IMO, I think the bets Riders who pulled out their forms in the Hesei era, is Kuuga, Agito, Ryuki, Faiz, and Blade... Basically, everything else dropped down the hill...
Kuuga's reasons for forms: STRONGER monsters and each forms are good with diffrent types of monsters, Pegasus forms for flying types etcs. Also, WILL POWER increases strength, not some Sword-Bat... Also, he has his own Ultimate Sword he never used. Basically, it's the strongest version of the titan Form's Sword, Rising, but black colorred...
Agito's reasons for forms: Basically, kinda like the same reasons for Kuuga... the El Lords were appearing...
Ryuki: He didn't even used his freaking Survive card in his last battle at all!!! He uses it for only important things!!!
Faiz: Eh? Accel Form was used when needed. So was Blaster Form...
Blade: Forms fits with the series plot and story about the deck of cards and monsters being up to 53 and also that each is a card... Course, it would have been easy to figure it out... King Form being used was also part of Kenzaki's plan on becoming a Joker...
The rest???
Hibiki: Keeps on using Armed Saber...
Kabuto: Hyper Zecter and stealing everyone else's zecter for his own "Perfect" Zecter.
Den-O: Was Climax Form needed at all!? I mean, I know the Taros dissappeared, but WHAT!? I mean, they could have just become Liner Form eqquipped to Ryotaro...
Kiva: No reasons... Except that Tatsulot only reacts to strong feelings, and Kiva's really expeiriencing strong feelings nowasayds...