As a Power Rangers fan I'd say MMPR Season 1 would be my favorite, for nostalgic reasons. I used to love watching Power Rangers as a kid and Season 1 would bring me back happy memories.
Today, I still enjoy watching MMPR Season 1, with pride. I have to admit, it's not better than ZyuRanger, but MMPR did have some of it's own good parts. Plus it's way better than these new Power Rangers series from Disney.
I still want to see Season 1 get released on DVD Box set. Unfortunately I heard rumours that Disney will never release it on DVD Box set regardless of popular demand. I have no Idea why, maybe Disney take too much pride in their own crappy work. If Disney aren't gonna do it, I hope at least someone does it, maybe Toei, but they'll probably only release it in Japan, meaning we'll have to import.
The show was still finding its voice in season 1. But the stuff with GWE and Lokar and the really cataclysmic stuff, that was awesome. All in all, it was a good season, particularly "Return of an Old Friend." You gotta love that cliffhanger... one of the best in PR history.