AK rr'ed pot OOP flop cbet? PS 100NL 6max

[ZingyDNA]

Table's been bit crazy. MP seems pretty tight, but hasn't made real postflop decisions. CO is LP, but I'm pretty sure he goes way if flop doesn't hit him.

PokerStars No-Limit Hold'em, $1.00 BB (6 handed) Hand History Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

SB ($104.90)
Hero ($102.50)
UTG ($149)
MP ($101.45)
CO ($160.05)
Button ($222.30)

Preflop: Hero is BB with A[img]/images/graemlins/club.gif[/img], K[img]/images/graemlins/club.gif[/img].
<font color="#666666">1 fold</font>, <font color="#CC3333">MP raises to $4</font>, CO calls $4, <font color="#666666">2 folds</font>, <font color="#CC3333">Hero raises to $19</font>, MP calls $15, CO calls $15.

Flop: ($57.50) 9[img]/images/graemlins/diamond.gif[/img], 3[img]/images/graemlins/spade.gif[/img], 9[img]/images/graemlins/club.gif[/img] <font color="#0000FF">(3 players)</font>

Hero ???