1st: CN City. That whole graphic package looked awesome! U could tell they spent alot of money for all that to work. I loved the crossovers between old & [at the time] new CN characters in a huge CGI city, combining all the popular scenary, landmarks, & towns of all the cartoons.
2nd: Powerhouse. So much novelty with those bumpers. I also loved how they used different color backgrounds for the timeslots, like for the morning, afternoon, evening, midnight, and holidays. The Up Next bumpers were cool too.
3rd: Check It/Dimenisional. Especially Check It 1.0. I loved the different designs & colors they used for that era. 2.0 [a.k.a. the YYEEAAHHHUUAA!! era] was lasy. 3.0 was a upgrade. 4.0 was OK. with the whole emoji thing. Dimenisional Era was a HUGE upgrade, with the 2D, 3D, hand-crafted, and CGI bumpers.
Last: Noods. This era is kinda underappreiciated by some, but I like it. The Noods could change into different characters was nice.