I don't mind any of the three endings, I just wished they'd picked one and stuck with only that one.
I think that would've been counter to the sort of tone W was trying to establish for Heisei Rider's second decade, though. The "multiple endings" thing is clearly a shout-out to the production style of Showa Kamen Rider, where the stories were approached more as a series of adventures than a closed narrative. It was not unusual in a Showa series for an evil organization to get defeated halfway through the show, just for another one to show up.
Likewise, you sometimes had "final villains" comparable to Foundation X only showing up for the last handful of episodes. Toei used that approach to Showa Rider to make the universe feel big and exciting, and to establish that a Kamen Rider's adventures were really an ongoing struggle. W essentially tries to bring that feeling back. How well it did that is debatable, but if the show just focused on one thing it would be a radically different type of show.
So why did Ryuki get multiple endings? Was there a huge backlash of the original ending or something? I'm curious.
The tl;dr version of the story is "It was a promotional stunt."
The long version is that Toei was trepidatious about doing Ryuki at all, because it was such a radical departure from the successful Kuuga/Agito formula. The show's early ratings were considered bad at the time (though they're much higher than modern Rider ratings overall), and there were rumors that the show would get canceled and replaced early.
Well, the movie comes out about halfway through Ryuki's TV production run. Ryuki's producers basically used it to try and hype the show with a "How will it end?!" angle, while being careful to present an alternate ending that wasn't what the TV show would do. The stunt worked. People who went to see the movie began tuning into the show a bit more regularly.
By this point in the series Ohja has debuted, and he immediately became the show's breakout character in terms of driving its popularity. The multiple choice special airs a bit after the film opened, I believe, and uses the different ending scenarios to keep hyping the show's plot and the idea that Ryuki will have a wild, unpredictable ending you've just got to see.
The actual TV ending is
probably the one that should be considered most authoritative, since it was
probably the one planned when the show was in pre-production. Unfortunately, the TV ending feels really bland and generic if you've already seen the movie and special endings (though it works okay on its own).