Doug and Rugrats were the staples of Nickelodeon for me. They were the peanut butter and jelly of TV shows. 1A and 1B, and it alternated with me as far as which was which. I became a Doug fan first, started watching Rugrats in 1994 when it was given the 6ET weekday slot leading into the 6:30 Doug airings. Eventually, I grew to favor Rugrats, if only because I'd seen all the Doug episodes about 10 times at that point, and the Rugrats episodes were still new, or at least newer to me. Then the shows were inverted in time slots (Doug 6, Rugrats 6:30), and since my family ate dinner at 6PM, I was only able to see the second segment/story in Doug, and that helped recharge my interest in it.
Think I took a couple month break from Doug altogether at some point, and when I finally came back to it and watched it again, I was blown away by how I could ever have taken such a great show for granted. Eventually, I developed the ability to block out my intricate knowledge of reruns as I watched them (I learned how to live in the moment and pretend the outcome of each story was always in jeopardy), and therefore I was able to enjoy both Rugrats and Doug reruns every time they came on from then on (and Doug was moved to 7PM in either late 94 or early 95 so I could see the entirety of both Rugrats and Doug weekday evenings).
I didn't get Ren & Stimpy when I was a kid, and it just felt too dark for my taste back then. I've gone back and watched some of the John K episodes and found them pretty funny.
Loved Rocko's Modern Life once I really got into it and started appreciating satire. That was when I was 12-15 years old or so.
Liked Ahhh Real Monsters at first, but I remember a kid in a class of mine asking me, rhetorically, "you like that show?" to which I replied, "yeah," but then started to think about it and realized I really wasn't too fond of it anymore. I think I just got sick of the concept. After that, I just stopped watching it.
Hey Arnold was pretty good, but I was never a huge fan of it, for whatever reason.
Back to Rugrats, though. When I say Rugrats, I'm referring to the Classic 65. The Paul Germain episodes. Arlene "c-word" Klasky fired him, and the show went down the toilet. The more I read about that woman, the more I despise her. It's not Dil that was the big problem. It was the writing. It went from a show written on an adult level to being the most juvenile thing on TV. Klasky wanted her baby show about babies, and she got it.