Back in the early 90's, Sonic was my favourite character out of cartoons, video games, comics, or anything. I loved both of the original cartoons, for different reasons. I rarely got to see either show though, so it was always exciting to watch it. I rented the videos from Blockbuster like crazy.
For a while I sort of bought into SatAM's online hype as the greatest thing ever, although when I got the DVD set and re-watched all of it I sort of realized that the writing wasn't nearly as brilliant as everybody thought, and it suffered many of the same problems as other action/adventure cartoons from the time. That is, a lack of interesting animation; stiff, rigid adherence to model sheets; and often a lack of cohesiveness between the dialogue and the accompanying gestures. I was also put off by many of the seemingly arbitrary changes they made in the second season. The music, character designs and Rotor's voice were much better in the first season (although Sally getting the vest wasn't a big deal).
Constantly reading "AoStH=suck, SatAM=gold" online for a few years sort of lowered my opinion of AoStH too, but when I saw it again I was surprised to find that the animation was actually often very funny, the voices were all hysterical, there was occasionally some amusing dialogue, and in general it could be a very entertaining show.
Sonic Underground always seems to get a lot of hate, and it was pretty lame in concept. As someone else mentioned though, apart from the songs it was a pretty fun show to watch. Sort of a similar atmosphere to SatAM, albeit with different characters. I don't know if I want to buy it on DVD though. I think it's pretty odd that in the late 90's, when the video game series was pretty much dead except for the upcoming Sonic Adventure, they decided to make another Sonic cartoon, especially one with such a weird gimmick. Did the out-of-left-field "Sonic is a prince in a band with his siblings" concept come from the fact that nobody at Sega particularly cared what they did with the character at the time?
I loved the Sonic OVA, or 'Sonic the Movie' as it was released here. Even with the weird dub choices (why did Tails have a stuffed-up nose? "Sawdik, I wadd you do cub ovah heah!"), I enjoyed pretty much everything about it. If only the DVD weren't so rare...
I was excited about Sonic X when I heard about it, and I watched the first dozen episodes, but I was pretty disappointed. I would've maybe liked it, if not for the annoying 4Kids dub, and the human characters. Really, without Chris and his grandfather, that might have been my ideal Sonic show at the time.