Quick SB hand

[RunDownHouse]

I think I goofed just a bit on this one.

Reads: BB - fairly tight and passive (only have maybe 30 hands on him. Didn't play many, and only aggressiveness has been when he had AA and flopped a set).

UTG: Loose, passive.

MP: Slightly loose, slightly aggressive. Will definitely be aggro with the better hands, but sometimes seems like she concentrates more on her holding than her opponents' likely hands (ie decent, but some misplaced aggression).

CO: Idiot, the type that loves to limp-reraise. The previous hand he got caught bluffing the river with 7 high, kicker doesn't play. It was sooted, though.

Button: Very passive, has called down with a straight on a non-pair, non-flush board.

Now, my question: is going for a check-raise mandatory on this flop? I feel like either MP or CO will bet if checked to over half the time, but they're the only ones I can count on to bet. I'd die if it was checked through and someone's trash-trash turned a pair higher than mine.

A check-raise would likely fold out anyone who hadn't put a bet/call in already, with the possible exception of CO. I know this is a lot of reads/nonsense for a fairly low-content 1/2 hand, so any responses are appreciated. Besides... I've got time, I suppose.

Party Poker 1/2 Hold'em (6 max, 6 handed)
converter

Preflop: Hero is SB with 6[img]/images/graemlins/heart.gif[/img], 9[img]/images/graemlins/heart.gif[/img].
UTG calls, MP calls, CO calls, Button calls, Hero completes, BB checks.

Flop: (6 SB) 3[img]/images/graemlins/club.gif[/img], 9[img]/images/graemlins/spade.gif[/img], 4[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(6 players)</font>
<font color="#CC3333">Hero bets</font>, BB calls, UTG calls, MP folds, CO calls, Button folds.