Would prefer UB always if it is SL. There is a sense of control you have with that seat. You can get down at stations, stand near the door etc without the tension of anyone coming and occupying the seat.
If it is AC as well will prefer the same. The biggest advantage i feel is the access to charging points. While sUB/SLB is also good, many trains do not have charging points there. so these days access to mobile charging points becomes a consideration