I grew up with Roscoe Orman, and I suppose that he will always be my sentimental favorite. I even got to meet him as a kid! But Matt Robinson is consistently very funny and edgy, and is probably objectively my favorite Gordon. He is all about improvisation and would be a completely different character if he were forced to stick to the scripted page... like the time Oscar slammed into his trash can and Gordon simply retorted, "Isolationist!"
Everyone has their favorite era, and that's fine. I personally prefer the first 14 seasons, although I still have some time for seasons 15-20. We all come to it with our own memories, so it's silly to assert your personal nostalgia as some kind of objective truth. It's not like we're sizing up the collective works of Shakespeare here.
Sure, season 1 could be a little repetitive. They also had to produce or at least procure every single segment you see on the show that year! All the subsequent seasons had the luxury of being able to draw from (by the mid 70s) a vast catalog of material.
Looking at the totality of what season 1 produced, basically inventing the format, all the new characters (human and muppet) that were created, and all the memorable segments introduced that remained in circulation for decades, is my preferred approach to evaluating it overall.