What are you really referring to "comments", based on likes? Do you mean that Avatar is your favorite show based on 75% comments?75 percent of these comments to be Avatar, 10 percent of the comments to be Hey Arnold, another 10 percent of these comments to be another 90's Nicktoon (Rocko's Modern Life, Rugrats) And 5 percent of these comments to be something else. Calling it.
Oh, and if you wanted to know. Tie between Avatar and Hey Arnold
Currently, I only watch Nickelodeon for Fairly Odd Parents, Legend Of Korra, and Teenage Mutant Ninja Turtles.
Before that, these are my favorite Nick shows:
Rugrats / All Grown Up
Rocko's Modern Life
Avatar: The Last Airbender
My Life As A Teenage Robot