My favorite has to be Season 6 because it's Doctor and the Ponds just having adventures and RIVER IS QUEEN.
But, my least favorite would have to be Season 3 because Martha wasn't a super interesting companion.. I did love those episodes where 10 turns human but..
Favorite season: Season 3, because Martha "Boss Ass Bitch who doesn't take the Doctor's shit" Jones and the Master were in it, or Season 5. Fetus Roramy and Vampires in Venice is what keeps me going.
Least favorite season:.. Hmm... Probably season 8, even though I love it, some of it just bores me. I get to see my queen Clara though so it's ok (◡‿◡✿)