Bet or check?

[TheCat]

Poker Stars $50 NLHE rebuy tournament.

Blinds are 400/800. 8 players on the table. I'm UTG 20K chips with AQo I raise to 2400, folded around to SB 22K chips, who calls, BB folds.

SB is new to the table and you have no read on him.

Flop comes three rags, SB checks.

Do I make a continuation bet or check and take a free card?

In the actual game I made a pot sized continuation bet. I think this was a big mistake as SB must have something. My raise UTG shows strength so he's got to be calling with something that has me beat.

What do you think?