Shade is probably preferable so the jugs don't dry out so fast. The seeds will still sprout--most of mine have been in the shade all along and I've got thousands of sprouts. I notice that so far the jugs in the shade are still plenty moist but the ones that get a few hours of sun have been drying out.
My jugs sprouted later than folks who put theirs in the sun but I figured it was better to have them in the shade for when they did sprout to avoid frying the tender wee sprouts.