Usually the SM STA will choose an AP with the highest RSSI and CINR values. If APs are added in the Preferred List and when the SM STA boots up it will follow the below procedure
1.The STA scans all the channels in the scan list, record the SSIDs, RSSI and CINR value of all the APs that it sees. It will then choose the AP with the best RSSI value.
2.If STA sees two or more APs with the same or similar RSSI values, then it will pick the AP with the best CINR.
3.If all things happen to be equal, then the third criteria is the channel bandwidth. The SM will pick the AP with the widest channel bandwidth.
4.If that is also equal across the APs, then it picks the AP with the lowest BSSID.
Once an SM STA picks an AP and connects to it, it will not periodically rescan for a better AP until it is disconnected. This feature is yet to be added in the future release.