How do you proceed after this flop lead, vs 3 different types of villains.

1) 26/17, regular who is pretty aggressive. Not sure if sc's are in his range or not preflop.
2) 19/15, TAGG reg. not tricky
3) unknown

Full Tilt No-Limit Hold'em, $4 BB (6 handed) Full-Tilt Converter Tool from FlopTurnRiver.com (Format: FlopTurnRiver)

SB ($1914.10)
Hero ($400)
UTG ($781.40)
MP ($402)
CO ($45.80)
Button ($97)

Preflop: Hero is BB with Q, A.
2 folds, CO calls $4, Button calls $4, SB completes, Hero raises to $28, CO folds, Button folds, SB calls $20.

Flop: ($60) 6, A, 2 (2 players)
SB bets $44, Hero ????????