Mine would be Juken Sentai Gekiranger and Engine Sentai Go-Onger

I'd say...Gekiranger has my first place vote, with Hurricanger in as a close second, and magiranger in third.

Magiranger was fun, pure and simple, and also incredibly heart warming.

Hurricanger...I really, really, really, really like ninjas.

Gekiranger has a very appealing storyline, to me, its own type of fun, and has Bat Ken of all things, which I find very splendid...also can't forget that the guy who played Rio was a hottie.

hmm,,, let me see....

from the old time ( 1970 something - 1999 ) :
based on the costume design : maskman
based on the story-line : jetman, turbo ranger
based on the overall average : oh-ranger

from the new age (1999-present) :
to be honest,,, i never followed any (except for the Go-Ongers) lol
but a watched their movies, though,, and IMO,, i'll prefer..
Gaoranger, Abaranger, Boukenger, and Gekiranger

my #1 fav is jetman! then gaoranger & hurricanger