I've decided to close this battle early, Skull and Caucasus move onto the Tourney!

Kamen Rider Similarities Battle Round 13: Holy Red Motorcycle, Batman!
 

This battle observes 2 riders who can take the form of something else, one similar to a Kaijin, and another that turns into a motorcycle-

Kamen Rider Kiva (2008)

VS

Kamen Rider Accel (Kamen Rider W, 2010)

And now for some facts
Kiva:

• Able to perform the Darkness Moon Break, a rider kick that shifts day to night
• Can shift into Garulu Form, wielding the Garulu Saber, giving him the ability to fight in a feral state while increasing his speed
• Can shift into Basshaa Form, allowing him to wield the Bashaa Magnum and control water, with his finisher being able to follow the opponent, due to his increased accuracy and marksmanship.
• Can assume Dogga Form, allowing him to wield the Dogga Hammer and control electricity, while also giving him super strength.
• Can blend the three forms and become DoGaBaKi form, allowing him to access the 3 weapons.
• Can attach the Buroon Booster to his motorcycle, allowing it to increase speed.
• Can summon the Castle Doran and Shoodoran, dragons to aid him in battle.
• Most Powerful Form: Emperor Form
• As Emperor Form, he becomes exponentially stronger, able to use Tatsulot to use several “Fever” attacks and can assume Flight Style, a dragon like creature known as the “Emperor Bat.”
• Wields the Zanvat Sword
• Weaknesses- Kiva may hesitate killing someone if they had befriended him, Kivat is required to access Kiva Form while Tatsulot is required to access Emperor Form, if either are incapacitated, he can’t fight. Dogga Form loses speed in favor of power, Basshaa form lacks power in hand to hand combat.

Accel:

• Has 3 forms (4 counting bike form)
• Wields the Engine Blade, which has 3 different attacks (Jet, Electric, Steam)
• Bike Form allows him to travel without the use of a Rider Machine, can combine with the Gunner A, to use a powerful shot, or a Maximum Drive using the Engine memory
• Most Powerful Form: Trial (TV), Booster (Movies)
• Trial allows him to move at fast speeds, giving him the ability to slash or hit an opponent multiple times in a small amount of time
• Booster allows Accel to fly at fast speeds
• Weakness: Needs Gaia Memories to Henshin, Trial takes away Bike Form and offensive power

This battle closes on the 4th of July!

Wataru would be too busy being emo in the bathtub. Terui for the win.

in the famous words of kivat bat the third..wake up!!

One minor stipulation: The Zanvat saber pretty much becomes Kiva's standard weapon at the halfway point. He has complete access to it even when not in Emperor Form.
Let's Go Kamen Rider even has him using it in his Kiva Form (Lol redundancy. Kiva's base form is "Kiva Kiva Form" :lol).
Also, he can still use his Arms beasts while in Emperor form (Though only Emperor Garulu appeared, it is possible for him to use the other 2, in addition to the HBV exclusive Emperor DoGaBaKi.)

Anyway, I'm voting Kiva. The early Wataru was a wimp and the mid Wateru was emo, but by the end of the series, he grew enough for me to think he could take Accel.
Power wise, Accel is probably stronger, with Booster's flight giving him a major advantage, but I think Kiva could take him out the sky. Trial's speed is another story, but his Death of a Thousand Papercuts style of fighting can be countered with Dogga's resilience.

I want to root for Terui, but end of series Wataru could take him I'd think.

Accel for me...again goes with experience plus frankly the Gunner A can be used independently for artillery strikes. I think he could out manoever Kiva in either upgraded mode. Plus you know The Chief would never forgive him if he lost to a pumpkin head...

This ones difficult, but I got to go with Kiva. I think Dogga form is enough of a tank to counter the rapid kicks of Trial form. Plus the fact he turns into a giant bat is awesome, and the way Tatsulot can power up the Arms gives him a big power boost.

I'm sorry but Castle Doran > Gunner A.

But it's Kiva, he wouldn't use Dogga form - he'd just go straight to Emperor like he always did. And frankly, Emperor is one of the weaker final forms out there.