Grunch.
The flop is where the important decision is imo.
We just flopped the gutter straight-flush draw which is just so awesome that I like raising it. The only hand I'm really afraid of is the NFD; if we raise it we can force it out. Our equity is fine vs. sets and made straights. Raising the flop also forces out the occasional one pair hand he's getting fancy with, and it gets him to fold 2pr hands sometimes as well. There are many benefits to raising.
The big problem with this line is you aren't getting folds from A
T
. If the top card was flushing, I'd say 3! the flop for sure, but since it isn't I'm also okay with folding. Calling is by far the worst option imo because we get stacked from better flushes. Calling is great when we have IO on our side, but as a rule I like to push non-nut draws more aggressively because of RIO.
I'm also advocating 3! on the flop because our huge (~50% no matter what) equity goes way down on the turn, and a 3! here looks super strong so we have to have some fold equity, and possibly a lot of it. Basically 3-betting looks automatically profitable here, much better than the 0 EV of folding, unless there's some crucial detail I'm overlooking.
So imo, on the flop, 3! >> fold >>>>>>> call.