We have a slide on a small (17') trailer. Main advantage,if not the only, is added space. A jack knife sofa sits in the slide.
We can access the bathroom and fridge when the slide is in, and use the camper withn the slide in. Which is nice if your going to spend a night in a parking lot where space is limited.
Slides are more prone to leaking. Winter camping, if you get snowed on you'd have to clean it off before retracting it, if the snow becomes frozen it's gonna make matters more difficult.
If i was going to look at a non-slide unit i'd want it to be 8' wide. I personally would have no issues with a non-slide unit if the floor plan suited our needs.
I know you asked about class b's and c's but thought some of my input might be helpful.