I guess Are You Afraid of the Dark too, but since it was a Canadian show that aired on a Canadian network here, I don't really consider it all that Nick-ish.
When I was a kid all I watched was Nick. Only watched Disney Channel for Suite Life sometimes.
So many shows. Rugrats, Hey Arnold, Fairly Odd Parents, Kenan and Kel, All That, Spongebob, CatDog, Rocket Power, ChalkZone, Ned's Declassified, The Amanda Show, Doug, Drake and Josh, Avatar, Danny Phantom, Rocko's Modern Life, Wild Thornberrys... Like ****
The only thing modern-day Nick has going for it when it comes to star power is Ariana. Jamie Lynn, Miranda, and Victoria all failed to take off. Disney has Selena, Miley, Demi, Bridgit, Zendaya, the entire HSM cast, Ross, etc.
I used both growing up. Rugrats was everything when I was a toddler. Nickelodeon to a lesser degree once middle school came around. That's So Raven alone>>>>