RMF at BJC is owned by our mechanic. We know because once in a while we have to wait for our airplane for the money makers to butt in line ahead of us for something. LOL! (Kinda kidding, kinda not. Greg is a good guy though and it's very rare. But his shop is very busy with paying customers and his own fleet these days.)
Others have joked about the "Aspen Borg", that would be Aspen Flying Club at APA. Not the best rates always but generally consistently good maintenance and the place has been run very well under Chris Dillis who started with a few Gobosh aircraft at KEIK and grew his business enough to buy the old Aspen as well as now at least one competitor. If not more. I don't keep track. But they're running that club pretty well as a business and not charging under what it costs them to maintain things properly, for the most part.
Which brings up a warning. At some of the smaller airports you'll find some "great deals". Ask around a bit and make sure you don't hear horror stories of deferred maintenance. Seems like every few years there's some school at one of the Denver area airports that only has two or three planes and offers prices that look too good to be true. Let me tell you, they are. All of those places have gone under and been reborn under new names multiple times.
Judging by the changes in the fleet at Independence Aviation at APA (and only that, I don't know em), Independence has branched out into more types. They were almost exclusively Cirrus only and are still heavily Cirrus oriented if you like those, and have the extra $$$ to fly them. Seems like a professionally run place also but I guess being an all Cirri shop wasn't working out or they just decided to grow a while back. Their fleet list is taking on various aircraft lately that scream "normal flight school" to me. They're hosts to the IMC/IFR/whatever Club at APA and host and run a number of FAASTeam seminars. They're much more active in the "safety" community than anyone else on the field, IMHO.
The above are just impressions from hanging around the airport for a very long time. But I'm not involved or active in the rental scene really. I just talk to folks and walk to the hangar and open it with my key and pull the 182 out and go flying. So grain of salt and all that.
Can't really recommend any instructors. Haven't spent enough time with any lately. Know two of the busy DPEs hat cover APA and they're always giving a lot of checkrides over at Aspen. Don't see much horn tooting about checkrides at the other places by that doesn't mean they aren't happening. Just poor marketing.
The instructor I liked at Aspen left some time ago when he got too busy teaching prospective airline kids how to do it the "flight crew" way in sims. And then moved overseas for a family issue or something. Anyway, kinda miss him. No BS guy. But he ain't here no mo'. So I can't recommend him.
I was poking around in my audio archives and found our podcast's interview with Chris Dillis back when he had just barely started to move one of the Gobosh aircraft from EIK to APA. Seems like forever ago now. I think one of them is hangared next door to our hangar. He's aviation crazy but also seems to have business sense. Aspen has done well under him.
I wouldn't hesitate to use Aspen for rentals but I would give a hairy eyeball to the larger numbered end of the fleet in the Skyhawks and look for the "lemon or two" that are in that group of airplanes and quietly avoid those. They're not BAD, but there's plenty to choose from.
In the higher end stuff they have very few problems with MX and upkeep *except* for their 182RG which finally skidded itself down the runway without a nose gear, on an FAA CFI ride, no less.
Retracts at APA: I hate to say this but be careful if you're going for your Commerical eventually.
They're few and far between nowadays and they've had the ____ kicked out of all of them.
Not really Aspen's fault on theirs finally getting whacked, nor any of the other clubs that have had it happen. There is very little grass growing under any of them when they're "up" and not "down" and Commercial students just beat the holy hell out of any nice retract that comes anywhere near my home airport.
That's all I've got. Good luck finding a good CFI and rental place.