Fourze. Definately Fourze. He has the raw firepower, he doesn't need another person to Henshin, and Space is in fact Awesome.

Oh man....I don't know who to pick. Fourze has the versatility of switches, but W has all the knowledge/strategy. Two? Or four? Hmm...........

I love Fourze and while he does have a lot of options, I'm going to have to go with Double on this because here two heads are certainly better than one.

Double is a better fighter than Fourze's straight brawling, the gaia memory switching in and out is more seamless than the astro switches (giving Double time to get in some quick hits with combos such as lunar trigger) and given the chance to properly research him, I'm sure Philip could find a way to take out Gentaro relatively quickly.

But in reality, these are two riders you'd probably never see face off against each other :lol

Fourze is far more versatile when it comes to switches and means he can be more unpredictable.
Double is smarter (Thanks to Philip), and can make better use of the few powers he has.

I'm going to give it to Double. His 9 forms and 2 Super forms (I'm not counting Fang/Joker because it requires a different body to transform into, and while swapping memories/switches are free actions, de-transforming, regaining consciousness, and transforming again most certainly is not) just puts him at a better standing than Fourze, especially when Fourze doesn't have Kengo on the sidelines telling him what switches to use (Because if Gen was left to it, all he'd use was Rocket and the various form states switches).

I'm going with Double. Not all of Fouze's Switches are combat based, plus Gen tends to use Rocket over more practical choices. Throw in Philip's clear head and Shotaro's willpower and this fight will swing to W's side, though Fourze will not make this a east win.

W. Fourze is versatile, but I think he comes up short when he has to deal with someone whose fighting prowess extends past gimmick spamming.

Onore Inoue!

Double because he has (say it with me, now)

RAINBOWS. OF. DEATH.

I do want to vote for Fourze but in this I think W is the stronger Rider here.

Oh man this is a tough one. Sheer power vs. highly skilled. The power of space vs. the knowledge of the earth. I have to give it to Double though.