Well thank you all (and hahaha at your comment KROOO). I'll probably just start with OOO, go through W, and then just start picking at random.

Beware of Decade. It spoils major plot points in Kabuto, Faiz, and possibly a few others.

My suggestion would be Kamen Rider Fourze. It's a Fun series with alot of humor, and a very good story throughout. I'd also suggest watching Kamen Rider Kabuto. It's another very good series, and it's a must-watch- for anyone into Kamen Rider.

I love Fourze as heck, but my suggestion for starting point is actually W, even before OOO. W represented a shift in Kamen Rider direction after Decade sort of rebooted everything. The post Decade series just felt different and they all feel more connected to each other than the pre-Decade series did.

W is also a good balance of goofy and serious, thus I see it as a prototypical modern Kamen Rider series. Fourze is my favorite, but it is definitely different in its focus on light-heartedness.

I may not be right in my analyses, but these are my reasons for recommending W first.

W and OOO are popular starting points and you can't go wrong with either. I'd recommend Agito, too, though, as it was the first show that really hooked me.

I started with Wizard, and am all nice and caught up on that, minus the newest episode (waiting on subs for that). I've always liked Kamen Rider, at least watching reviews of the various figuarts from people like TJ and Vangelus. Wizard was what really interested me in watching the series though. I had some passing interest in Fourze as well, I thought the suit design was...a bit silly (mostly due to the rocket head), but I dug the whole module/switch thing so I ended up getting the Figuart of his base states, which got me interested in watching the series. I'm up to episode 15 there and have been enjoying it.

OOO is what got me into it

I started watching Wizard because I loved Flame Style's design. I find it's a pretty good show, although it's still ongoing. From there I watched W. Great story, amazing characters, especially Shotaro and Wakana. It's a nice balance between humor and seriousness. Then I watched Fourze. I actually tried getting into it when it first started, but the silliness REALLY turned me off. Luckily that drops off quite a bit after the first few episodes and Meteor ended up making the show for me. Then I started Den-O. Not as lighthearted as Fourze, but still a silly show. However, I feel like Den-O is so over-the-top in concept alone that the silliness works to its advantage. Finally I started OOO, which I have to say is my hands-down favorite. Eiji is a compelling main character, Ankh's personality and motives are cunning and complex, the fights are excellently choreographed, and the dynamic between Date and Gotou after Birth's appearance is spectacular.

I might get some flack from this, but start with Decade. It has a very gripping story, the series is absolutely epic and it acts as a history lesson for Kamen Rider all be it a slightly inaccurate one. It also leads into W which is another great series.

I agree that it's a decent starting point.
But a gripping story? Lol no. There is no story. Everything the series builds up to leads to absolutely nothing. Literally. There is no resolution. The opening scene is the ending scene. Diend shooting Tsukasa was retconned out and doesn't have any bearing on the follow up movie audiences were supposed to see. The hints of what Tsukasa might really be is never resolved. He just is.
History lesson? No. It just parades the suits and spoils one of the twists in Faiz.
Leads into W? Heh, no. Double and Decade aren't connected. Double showing up in Decade's movie isn't proof of it. It just means that Double appeared early.
Decade is a terrible, terrible show that's only value is it's reduced length and it lets you see the previous 10 Heisei suits in action (And it spoils Faiz, meaning you don't need to see Faiz). A couple cool fights and scenes here and there does not redeem an entire series and make it good.