personally, I'd avoid a jigsaw if at all possible. my experience is the blade walks around too much to make a smooth, consistent cut. Even the nibblers walk. but i think nibblers, plasma torch, or even a pneumatic cut-off wheel would be better than a jigsaw.. aviation snips may work if it isn't too thick, but man you will have popeye arms when its all done.
I agree with most of what you said. But a nibbler would do a fine job if you want a perfect circle cut using a radius guide. Without a guide, the cut would be a bit uneven.
What I'd do is rough out the cut with a nibbler if a radius guide isn't available and go back in with aviation snips for cleanup to the final line. There's no way you could cut a 16 gauge bedside with aviation snips in one pass, because the waste has to be bent out of the way, and more than about 1/2" waste would be impossible to roll unless you're doing a straight cut, and even then I'd have my doubts. For straight cuts a jump shear or hiring it out for long cuts would be the way to go.
I agree about the popeye arms.
[on edit] That part that Robert said about the 1/4" waste (view Bill's how to video) is important. If you have more than that, go to something besides aviation snips.
