If you are looking to maximize points, the CY is by far the best choice. It is one redemption level lower than the Aloft but a much nicer hotel. It is in a great location near both BTS lines and is quiet and clean. It is actually pretty near the SR geographically and a world away from Soi 11 figuratively. You can walk to the malls from the hotel on wide, relatively quiet sidewalks. The staff is great. It is very different from NA CYs: more akin to American FS hotels with a restaurant, CL and full-time busmen manning the front door.
If you pay enough points to go up one level on redemption, the Soi 57 Marriott is swank, in the cool Thong Lor area and a short block from the BTS station. The staff is awesome. It is my favorite of the Cat 4 properties in Bangkok.
Yes, the SR is very nice It is also Cat 5 but relatively inexpensive for cash, making it a non-economical hotel for points redemption.