with 5 CT's I would;
2 @ A, close or on bomb site, when looking at short A covered by crates from long A and vice versa
2@ B One near doors, one tucked away
1 remain in spawn in the dark, watching middle and ready to come and crossfire long and short A
That way everyone is covered. I like TL's idea of holding site rather than getting sniped. There should always be two guns relatively quickly on any sightings.
(http://www.angelfire.com/tv2/jimmyspage/dust2.jpg)