That's a real toss up for me. Just incredibly difficult to narrow it down to one. But Gekiranger, Dekaranger, & Gaoranger should all be in the running for the #1 choice.

Having finished Kakuranger since making this post, I can confirm that Gekiranger is still the greatest.

From what i've seen (all of Zyuranger, half of Jetman and Megaranger, less than 10 episodes of Gokaiger, Dairanger, Timeranger, Carranger, Battle Fever J, Gekiranger, Goranger, and Kakuranger) Jetman is my favorite, followed by Zyuranger.

I've watched Gokaiger, Kyoryuger, Shinkenger, Dekaranger, Kakuranger and Zyuranger. My favourites have to be Shinkenger and Gokaiger, but that said I have enjoyed the ones mentioned (couldn't get into Gobusters and Toqger, though I am watching it every week, I don't feel anything for the main 5 characters.