Really you can use pretty much any of these halloween costumes to turn into a Pred skin. Some are more popular than others like the Mr. I suits, but since your just using the costume for the basis of a latex skin, it really comes down to which you prefer to start with and your budget. You can go with the already muscled costumes to save time, or a plain non-muscled suit and build your own muscles into it, it's all up to you and the amount of work you want to put into it. I just started a Pred skin and I'm using a somewhat basic Superman costume I got online. It had a somewhat muscled chest piece that I expanded with cotton pads and cotton balls to give even more detail to the skin, and once you start latexing it, it really doesn't matter what you started with underneath since you have free reign during the building and latexing phase to do whatever you want to alter the appearance. So just pick something your comfortable with price wise and appearance wise and have at it!