Fuji pro s... pro h if you need the speed. The fujis will handle the slightly mixed light quite well. 12x12 and 16x16 are not the slightest challenge for them or any other recent colour print film; pro h can handle that well too and you may actually prefer the contrast.

In general, scanned colour print films will appear grainy in the shadows if you don't expose sufficiently. So... as usual, err on the side of slight overexposure.