Here’s my ranking:

Season 2
Season 3
Season 4
Season 1
Season 5
Season 7
Season 6

2
3
1
4
5
6
7

Although season 2 and 3 are so good its hard to separate which is better. After season 4, it just jumped the shark. The writing got so dumb and the scripts were written like Cheers where every line spoken has a laugh line. Because of that, the character development suffered and they changed. Its still a good show but I have no interest after season 4. But that's the case with almost every show. Very few shows can keep that level after 4 years.

Season 3 and Season 1 are tied.

Season 2

Season 4

Season 5

Season 6

Season 7

2
1
4
3
5
6
7

like others, I do feel like 5-7 are a big decline from 1-4, but I still like all of it, but the majority of the classics come from 1985-1989