For me, it'd have to be:
Gekiranger
Gokaiger

Because those are the only two series I've finished :lol
I've began plenty of series (GoBuster, Magiranger, Boukenger, Goseiger, Go-Onger, Sun Vulcan, and Shinkenger), but none of them held my interest for beyond 20 or so episodes (If even that, with Shinkenger being the only one to exceed 10 episodes).

Currently watching Go-onger. Not the best Sentai show I've watched, but one or two really good episodes keep me watching, and the team has heart. I'm reaching the introduction of Gold and Silver, so I can't wait to continue.

I'd advise keeping up with Shinkenger, it does get better after loads of filler. If anything the last 10 episodes make the series for me. I understand the boredom in the beginning, though, as Doukoku does nothing significant at all initially.

Magiranger is also worth watching, as the story arcs get better over time for me. The final arc was very much worth watching.

Funnily enough Gekiranger for me is a series I lost interest with after about 4-5 episodes. Would you recommend I give it another chance? I find the Rangers themselves rather bland, and Jan is really annoying.

Jan is super annoying.
But GekiRanger is a great Sentai. The plot starts up when the 5 Deadly Venoms die off (Like, episode 12 or something) and never stops from there. I particularly loved it because the plot follows both the heroes and the villains, and doesn't just cut to the villains to show them plotting and then bitching when their plot fails. You follow Rio's story just as much as you follow Jan and the other Gekirangers' (Though Ran does kinda get left out...).

For Shinkenger, yeah. Once the feeling of "Wow, these designs are cool!" wore off, I got tired of it quickly. I'll try to give it another chance.
MagiRanger...Eh. I'll see.

Go-Oner is one of the shows I love to death for the absurdity of the Mecha and the awesome suit designs. Its not the strongest sentai but I do still love it.

I still haven't been able to push my was through Shinkenger though. I made it to episode 26 and just can't bring myself to care anymore. It just gets so boring in the middle. When my least favorite character is the Red on the team, I get worried.

Go-Onger gets much better with the introduction of gold and silver. It never really grows into an amazing show but I still found it to be a particularly memorable watch. Like Den-O says the absurdity of it is what makes it so enjoyable.

You definitely should give Gekiranger another chance though ComicGuy, the 3-piece team aren't great but Rio and Mele more than make up for them. And then Gou is an utter badass.

There you go, Tama. Fixed it for you :thumb:

You wish :lol

Love how you focus on the change, and not the fact I accidently called you Sentai Tamashii xD

I find that the main weakness of Shinkenger is that everything rests on Takeru. He holds and breaks the entire team. Because of that, all other Rangers are absolutely secondary in comparison, which can be a good or bad thing. He is literally the definition of a starring Red. So you love or hate the show based on him.

I must say, he gets some good character development towards the last 10 episodes, again, but I understand that it might not be worth waiting that long.

It is sometimes a shame that the rest of the Shinkengers, while having excellent character development on their own rights, are less memorable as a result of this secondary status. Other shows like Gokaiger focus on their Reds too, but not to the extent that the rest of the team falls to the sidelines. It's really like Timeranger, which focuses on a Red, Pink and Fire, which I attribute to Yasuko Kobayashi's writing style.

Well, Gokaiger's shortcoming, character-wise, was just lack of growth.
The Gokaigers got backstory and personalities, and that was it. Don got something later on with the faked article and junk, but the others just had character quirks to lean back on (For a perfect example of failed character arcs, look at the entire Joe/Cid/Barizog thing. Joe learns Barizog is Cid, learns transformation is irreversible (In the same episode, I believe), climatic fight 20 episodes later. That was pretty much it :\).

But yeah. Gokaiger did have a problem with putting too much emphasis on Captain Marvelous. All the Gokaigers were pretty much just Marvelous's yes-men (Seriously, did anyone, at any point in the series, ever disagree with Marvelous's decisions? I think Joe did...Once.)