All good points above.

If you can see through the marketing-speak, you can kind of make sense of how each brand is positioned here: Choice Hotels - Brand Information

Here's how I think Choice would classify each brand's image, in top-down order and based on the standard "STR Chain Scale" list:

Ascend - full-service boutique upscale
Cambria - full-service upscale
Clarion - full-service upper-midscale
Comfort Suites - limited-service upper-midscale
Comfort Inn - limited-service upper-midscale
Sleep Inn - limited service midscale
Quality Inn - limited service midscale
MainStay Suites - limited-service midscale extended-stay
Econo Lodge - limited-service economy
Rodeway Inn - limited-service economy
Suburban Extended Stay - limited-service economy extended-stay

Here's how I would actually rate them and describe their brand identity:

Cambria - upper-midscale, full-service, new construction, large rooms, modern decor and identity, very clean
Ascend - upper-midscale, full-service, boutique city-center and often historic conversions, can range from meh to surprisingly nice
Comfort Suites - midscale, limited-service, often new-construction or extensively renovated, good/tight brand standards and spacious rooms
Sleep Inn - midscale, limited-service, all-new construction and very tight brand standards, very consistent experience; only downside is rooms tend to be small and bathrooms are an odd layout
Comfort Inn - midscale, limited-service, loose brand standards, can range from downright filthy to quite nice (upper-end newly renovated ones typically have a similar decor and feel to a Comfort Suites)
Quality Inn - midscale, limited-service, loose brand standards, similar to Comfort Inn and mostly used to allow nearby franchisees to compete with each other without duplicating branding; target is slightly downmarket of Comfort Inn, but it really comes down to reading reviews and looking at pictures to choose
MainStay Suites - midscale extended-stay, limited-service; I think I've only ever stayed in one, and it was perfectly roomy and fine, but all extended-stay brands (even the more upscale extended-stay chains, like IHG's Candlewood or Staybridge brands, tend to attract a slightly seedy clientele)
Econo Lodge - economy, limited-service, extremely loose brand standards, can range from perfectly fine and serviceable to unclean and unsafe even with the door locked and latched
Rodeway Inn - economy, limited-service, extremely loose brand standards, similar to Econo Lodge and (like Quality) mostly used to prevent brand confusion between nearby properties. A friend and I stayed at an amazingly nice Rodeway just west of IAH and we still laugh about it being the world's nicest Rodeway!
Suburban Extended Stay - economy, limited service, loose brand standards, usually actually nicer than most Econo Lodges and Rodeway Inns, but the extended-stay element adds a seediness that tends to make them less appealing

Anything on my list from Sleep Inn or above, I am usually perfectly fine booking it sight-unseen, since the brand standards are tight and the risk of a bad experience is low. All else being equal (rates, location, and a cursory glance at the reviews on Choice's site), I'll probably book in the order listed (Cambria first, then Ascend, then Comfort Suites, etc.). Anything from Comfort Inn and below is one I have to actually read through the reviews and check photos both on Choice's site and Expedia and TripAdvisor before deciding where to book. All else being equal (similar reviews, similar location, same price, etc.), I'll generally favor Comfort over Quality, but it doesn't take much to change that (i.e. I'd much rather take a 3.5-rated Quality over a 3.0-rated Comfort). I haven't yet figured out whether Econo Lodge or Rodeway is positioned higher; they're both so variable in quality that I think it just comes down to the individual hotel. I usually avoid the extended-stay brands unless they get better reviews and have better prices than the standard brands.

I will say that despite having stayed in probably hundreds of Comforts and Qualities, I've never noticed a substantial difference in their breakfast offerings, but thinking back now after having read sdsearch's post, I can kind of see it. Still, give me a bowl of cereal with whole or lowfat (NOT nonfat!!) milk and I'm perfectly happy for the morning.