I would say try working with both - pepakura cardstock AND foam. You'll see what you prefer using more. Both have pros and cons.
And mostly people recommend using the way they prefer to, but it may not suit you, that's better to try it out yourself.
Best start out with smaller or pieces that are not too complicated.
Personally I prefer pepakura cardstock.
There are tons of tutorials for both cardstock and foam and even many building threads have interesting and helpful content that's worth checking out.