Depends on the age of the property and the location. Like many things.

RI gets you (generally) full size fridge, microwave, free breakfast, etc. - can be nicer if the property is new or newly renovated enough.
A lot of the Springhill Suites are newer and still free breakfast so I pick those.
CY depends on the property age, a lot of them in the US market are older. The Bistro kind of sucks without breakfast, but it might be more tolerable with free breakfast. However even if breakfast is free, the Bistro can be slooooow. Likely more of a problem during the breakfast rush on Mon-Thurs at locations with a lot of business travelers, especially since 50/75 night levels in new programs will have breakfast voucher as an option for welcome gift.

I tend to avoid CY unless the property is much more newly renovated. Some of the older ones can be pretty dire.

As others have already pointed out, proximity can be key. Nearest CY to my employer's major office is 12 minute drive, nearest full service is 25 minutes in ideal traffic, and up to 45 minutes in rush hour traffic. That extra sleep counts a lot even though the CY and FS Marriott have similar rates.