These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
General Ironicus liked Mil, due to how he looked like a human Sonic OC. It got to the point where Ironicus was calling Mil "Tails" in the last few parts.
The student known only as "Goth" is also pretty popular. As stated in Chip Cheezum's riff, at least he actually does something different instead of punching people right away. Another reason is mentioned above in Crowning Moment of Funny.
The Bald Teacher from the first season has also gained a following, mostly because the person voicing him was named Sephiroth in the credits.