My first rider series was OOO and I Still love it to this day but sadly it has become my second favorite due to gaim being so B.A

The honor goes to Ryuki, which became and has remained my favorite Rider series after the viewing.

Blade.

W was my first rider show.

in my case the honor goes to wizard......about a week after watching madoka magica....the similarities were quite noticeable which makes me think what the show would have been like had gen urobachi worked on it

W/Double.

Gaim was my first. Loved. It.

Kiva.

I have seen a bit of Ryuki/Faiz/Blade on my TV and was interested in Power Rangers from a young age.

Then, Decade got me into Rider as I watched some of the awesome footages then I watched the second half of Den-O because I was dumb at that time.

The first series I actually completed is OOO and I enjoyed it - planning to rewatch soon.

That I completely finished was OOO, the first show that my friend showed me to get me into it was Wizard. He reminded a lot of Viewtiful Joe and I loved Masked Rider when I was a kid so it pretty much a no-brainer for me that I got hooked on Kamen Rider.