Call. In a three-way pot like this, you should not raise the flop with a flush-draw when the ace is not of the flush suit. Change the flop to A-9-7, so you are hitting to the nuts, and you can consider a raise. The problem with this flop is that you can get buried if one of your opponents has the A with another club, giving him top pair with a better flush-draw. He will be pounding the pot having both the best hand and the best draw. Another reason to avoid raising is that it may not be in your best interest to drive out players when you have a drawing hand like this. They should be encouraged to hang around with their pairs and straight-draws so you get better pot odds, and have a chance to collect some additional money when you hit.