monopods allowed?
I would say, high ISO and low f-stop. But be wary of the low fstops, as you quickly decrease your DOF the lower you go.
If you had to choose between the 2 lenses, I'd go with the faster one [f/1.8], you at least have the option of f/1.8 if you REALLY need it). If funds allow, perhaps a fast lens w/ IS is in (on) order.
Although I try to keep the ISO as low as possible; my philosophy in situations like this is that a noisy, focused shot (plus the noise removal sw/plugins we have nowadays are pretty good) is better than a noiseless, OOF shot (there is only so much you can rescue with USM).