If you definitely don’t want to go to Armidale (which is not something you have any control over), then you’ve probably answered your own question.
What I’d probably do is put JMP first preference. See what happens after first round offers come out. If you get Armidale, rearrange preferences and keep fingers crossed you were also eligible for UNSW and will therefore get offer in next UAC round. We’ve heard from multiple sources that it’s basically impossible to have your campus switched for JMP.
Also, don’t forget there’s a chance you get Port Mac at UNSW.
If they were eligible for UNSW wouldn't they receive definitely receive this offer in the next round?