Beast Wars/ Machines absolutely no contest.

 

1 - Original G1 cartoon
2 - G1 Japanese continuation - Headmasters/Masterforce/Victory
3 - Robots in Disguise 2001
4 - Beast Wars II

I don't like anything else even half as much as I like the stuff on the list above.

 

Animated was the most memorable and enjoyable for me.
Beast Wars was a close second in all aspects, but not as memorable, in my opinion.

G1 was fun, at times, but boring for the most part.
Prime is basically like the Bay movies, too grey, gritty and unentertaining for me. It had a couple of cool scenes but the one-dimensional characters ruined almost everything in the show, and those horrible and unnecessary human characters just made it worse.

I feel like Transformers is at its best when the writers understand how silly the concept is and just roll with the fun nature of everything, which is what TFA and BW did.