For me a lot depends on how well they can sustain the writing over the season. Some of the longer running seasons, hell, even some shorter seasons had episodes that are clearly filler because they had a fixed quota of episodes but not quite enough script and/or budget to cover all of them to the same standard.

I think most people will be familiar with the Breaking Bad episode Fly, which is the worst rated by some margin on the entire show. It had its budget stolen for the episodes around it, and frankly it sucks. It would have been better if they just went one episode less that season. This is why I am in favor of the show only having enough episodes that it can actually sustain with great content, and may be that number varies season to season.

Monster of the week shows like Buffy that have a season long big story arc and usually single shot weekly stories it is even more important not to over do it with poor quality filler. and over stretch the big story arc to the point it becomes boring.