Hey, finally I can provide some value on this board!
TL:DR: Ridgecrest is the best course, but Shadow Valley or Quail Hollow give a unique experience.
Ridgecrest - Links style muni with a fun mix of holes especially on the back nine, great use of a hillside bench, and interesting green complexes. Very playable and usually in good condition. Down side is that the location isn’t anything interesting and the front nine is interstate adjacent. Very walkable.
Shadow Valley - Unique course in the foothills uses the elevation but not severely, usually in great condition. Back nine has some more generic parkland style holes but overall a fun course. More forgiving than quail hollow, less dramatic elevation. Pretty walkable.
Quail Hollow - former private course that was donated to the city a few years ago. Accuracy is a premium off the tee and the greens are severe. Only a par 70 but playing from the back tees puts some length and driver in play. Uses the elevation to the extreme and plays up the sides of the canyon walls throughout the course. Not a fun walk unless your glutes are super activated.
Falcon Crest - Probably the truest (public) test of golf in Boise, out in the pasture land south of town. Overall a solid course that has some holes that can really kick you in the mouth if you don’t hit multiple good shots. Mosquitos are horrible here at times, way more than any other course in town.
Others:
Banbury - Same designer as Ridgecrest and plays similar but more penal with water everywhere. Used to be in better condition, now just good but overpriced. Hosted USGA Girls Pub Links in the early 2000 and coasted on that ever since.
Redhawk - Fun 6 holes in an old quarry, the rest is generic subdivision golf.
Warm Springs - My home course, muni closest to downtown. In need of some heavy tree control. Could be any parkland course you’d find across America.
Enjoy your time here, September is a great month to visit.