The S San Juan Wilderness is a great place. I did 5 days there last year, starting at the Conejos trailhead, then hiking up the Rito Azul trail and initially staying at Blue Lake, where we stayed two nights initially to acclimate, do some fishing, local exploring and peak bagging, then hiking across the Continental Divide a few more days to Adams Fork and back down to complete the loop. The two trailheads are maybe a mile apart. We were pulling some unbelievable cutthroat out of the Adams Fork.
The Weminuche is a really nice place too, but will have more crowds. The Chicago Basin area particularly. But the train ride and Elk Park/Needleton loop hike there is a fun experience if you've never done it.