I think Adventure is hanRAB down better than all. I watched all 54 episodes and loved it, it was fresh, interesting and enjoyable.
With Zero Two...I enjoyed the entire Kaiser arc, but found many of the episodes after that point boring and repetitive. And I won't even TOUCH episode 50....I can barely make it through any episode post Oikawa's introduction. To quote a friend, "just go away, Oikawa. No one likes you."
I thought Tamers was a very interesting season, suitably darker than the previous two, and much more realistic. The previous two seasons were clearly written mostly with children in mind; this one took the concept to a new level with more mature concepts.
And Frontier....I'm a bit erabarassed to admit I liked at least part of it, though I think it was second to 02 for the worst.
I never really have watched Savers, as I mostly haven't had the time. I do read online comparisons, though...