Avoid Hibiki and the Showa Riders until you have a feel for Kamen Rider. The former isn't like Kamen Rider at all and the latter can be boring if you just jump right in.
I'd say start with a modern Hesei Rider - Either Double or Ryuki.
Showa Rider series are good - they have their merits. But the earlier ones definitely do have signs of ageing... why? Cause it's a one-pattern, simple episodic series that isn't really that fun to marathon. It's a little more interesting when you have a grasp of the history to actually see the original characters and monsters in action. (I'm not saying the series are bad, but seriously, don't tell me the first series was particularly exciting all the way through)
Regardless, the best Showa Riders are Skyrider, Super-1 or Black (which is more modern in it's approach). Amazon is short and sweet, on the other hand, but it still follows the one-pattern approach I listed above. Shin, J, ZO are all 40-60 min movies that might further your interest in Showa era Riders.
That brings me to Decade. Decade - despite being a terrible show - showcases every Hesei Rider prior as well as having some tribute movies regarding Showa characters. It may be a good way to be exposed to a lot of Riders at once, and from there you could see which series interests you the most. (all the stories are changed, but the themes remain unscathed).
As for Hesei, these are my personal opinions:
Kuuga: The best of Kuuga is probably the best of Kamen Rider in general. The main character has a good motivation to fight, as well as good development and an evolving relationship with the secondary character. Overall, villains are scary and the two-part episode approach works pretty well. Unfortunately... Kuuga can be really boring. It gets pretty slow at times, and there isn't much of an intriguing, moving plot going on. Still, it is a good show.
Agito: Probably the best Hesei Kamen Rider, Agito has a deeply-involving story. It is intriguing, full of mystery, and is full of unique characters (the first to have three Riders in a show). Agito was just... dayum it was good.
Ryuki: Having grown up with Ryuki, I'm probably a little biased. But Ryuki is spectacular. If you like Den-O, Kobayashi (the writer) also wrote this and OOO so there are a lot of similarities between them. Anyway, the premise is that there is a Rider War taking place in a "Mirror" dimension and the protagonist is reluctant to participate. An interesting dynamic between the two lead characters paves the way for some extremely dramatic episodes that are pretty emotionally fuelled (don't get me wrong though, it still has comedy, just it gets messed towards the end)
555: The best Rider design of all time. Faiz... is a badass. And the technology gimmick is just the coolest idea they've ever come up with. Storywise, same writer as Agito so there is the same intrigue and mystery surrounding the characters that makes it really fun to watch. Unfortunately, while adding drama, the characters are all written to be unlikable, and they NEVER EVER converse with each other, causing all sorts of misunderstandings that make this frustrating to watch as well.
Blade: Blade is my favourite series because 1.) Every character has a good amount of development. 2.) Plot moves non-stop after the first 15 episodes (which are fairly slow- Don't let that turn you off!) 3.) Kenzaki is the best hero in the whole series, and 4.) The ending is the best you'll get in Hesei Kamen Rider.
Hibiki: Skip this. Watch it when you are used to regular Rider seasons. This one is so different, focusing on a teacher-student relationship with the Rider business happening as a side-story. Also, there is a staff change that pretty much ruins the series around episode 30, which pisses a lot of people off.
Kabuto: Good, dumb fun. The story isn't anything all too special, partly because it is messy and has too much going on for it to handle, but damn! The characters are so much fun. They are gimmicky, hilarious, and their interactions are super over-blown and entertaining. Also, the Rider suits and action scenes are among the best in Kamen Rider altogether.
Kiva: In Kiva, Otoya Kurenai has his story told in 1988, while his son Wataru who becomes Kamen Rider Kiva has his story in 2008. This is a really cool approach, and brings a new level to foreshadowing and plot developments, as well as excitement to see how characters in 1988 come to be how they are 20 years later. Unfortunately, story is plagued by the same problem 555 had, as well as a shoddy romance side-plot and several sheering plot-holes. Cool theme though.
Double/W: Oh man, this series is SO much fun. It's everything a Kamen Rider should be, and a great intro to modern Rider. W is awesome, Accel's side-plots are awesome, the characters are awesome, the villains are awesome. Everything (minus the rushed-ness of the ending and Akiko) is pretty much awesome.
OOO: I really like this series. If you want to watch it, you probably would have made a good choice. Same writer as Den-O, as I mentioned before, so a lot of similar traits and themes. The two leads offer a fairly complex and well-acted relationship. The series kind of lulls on for a bit in the middle, but it's not that harmful considering the ending is one of the best.
Fourze: Dumb, good fun. If you like high school dramas, this may be worth it. Like I said, it's fun, but it's not particularly well-written and the plot isn't extremely intriguing. Though Kamen Rider Meteor is probably my favourite Rider of all time. Seriously, a total badass.
Wizard: Slow, but great fight scenes. Not done yet, but can't say much of about it as a whole. Anyway, it is a good series to watch on a weekly basis. Maybe you should start watching new episodes weekly starting with Gaim?
Anyway, those are my two cents. Have fun with Kamen Rider!
If you don't want to go back in time, then skip the "Showa Era" ones. If you want a more of a today's version, then start with the "Heisei Era" ones. I enjoy them all so it's a win, win for me. 
