If you are playing against a smart opponent they will ban Kongo so that they don't have to fight Jiggs there.
Generally Jigglypuff likes big stages with big blast zones and a high ceiling. What you want to strive for is a stage with both but this isn't always going to be the case in which case of the 2 a bigger stage is more important.
So basically; Big stage with big blast zones and high ceiling > big stage > big blast zones for Puff's best kinds of stages.
From that list Kongo is the best but as I said it will be banned against you by a smart opponent. After that stage I would say you best stages to go to would be Battle Field, Wuhu Island, Skyloft, or Duck Hunt. Duck Hunt is a really good stage to goto against characters who can't jump very well/have problems getting to high problem so that you can just camp out on the tree (this is basically as a way to replace Kongo when you're going up against someone like Mac or Dorf). BF/WI/SL is basically up to your discretion in what you prefer but for a quick thing into them;
BF is good because it has a rather high ceiling and that platform layout is helpful. It is basically a poor man's Dreamland when Dreamland doesn't exist.
Wuhu is good because it is usually a big stage throughout the traveling portions and transformations and most of the layouts are helpful for how Jiggs plays.
Skyloft is good for similar reasons that Wuhu is.
