Bet out on the river or go for a checkraise?

[PantherZ]

It's my second hand at the table, and I don't have any notes on the three opponents.

Party Poker 2/4 Hold'em (7 handed)

Preflop: PantherZ is SB with 9[img]/images/graemlins/heart.gif[/img], 6[img]/images/graemlins/heart.gif[/img].
UTG folds, MP1 folds, MP2 folds, CO calls, Button calls, PantherZ completes, BB checks.

Flop: (4 SB) 8[img]/images/graemlins/club.gif[/img], A[img]/images/graemlins/spade.gif[/img], 7[img]/images/graemlins/heart.gif[/img] <font color="blue">(4 players)</font>
<font color="CC3333">PantherZ bets</font>, BB folds, CO calls, Button folds.

Turn: (3 BB) 5[img]/images/graemlins/diamond.gif[/img] <font color="blue">(2 players)</font>
<font color="CC3333">PantherZ bets</font>, <font color="CC3333">CO raises</font>, <font color="CC3333">PantherZ 3-bets</font>, <font color="CC3333">CO caps</font>, PantherZ calls.

River: (11 BB) K[img]/images/graemlins/spade.gif[/img] <font color="blue">(2 players)</font>
<font color="CC3333">PantherZ ???</font>

Looks like he's got 2-pair, with a smaller chance of a set with 88, 77 or 55. I would hate to check and have him check behind, which he might do if he has Ax or 87 for a small two pair. If I bet out, he will certainly call and he might raise, giving me a chance to make it 3 bets.

What do you think. Bet out or go for a checkraise?