I do thing on average CYs are just a bit better than Fairfields and Springhill suites in terms of furniture, bathrooms, etc. Though this is to a large degree offset by the fact that many Fairfields and Springhills seem newer. I'd rather stay at a Fairfield or Springhill than a CY on average because of the breakfast, not just because its free, but I find a buffet (pre-pandemic) much faster which is good when I just need a bite before I head out to work. I guess the nice thing about CYs that they have an on-site bar and restaurant, which even if not amazing, gives you a way to drink without having to drive (assuming suburbs). This is US CYs only, many Asian CYs are really nice and do have breakfast. I will note that if you don't have status, I'm not sure people see a difference between CY and lower end FS hotels which also don't have free breakfast.
Sheraton, as you mention, is really the black sheep. I avoid any sheraton v. any FS marriott unless I actually know it is a good hotel. I've had so many mediocre or worse sheratons that feel like they haven't been renovated since the 1st Bush administration. That said, if they do have a CL, they tend to have a slightly better breakfast than the select service hotels. There are good Sheratons, but man, so many need a refresh stat.