I could go for the foldable design. I like that it could be a small 4" display that is easy to use in one hand and then open up to be an 8"ish tablet. What I think would be really, really cool though is a phone that combines the two concepts. It would look like a normal phone, but then one side of the bezel could pull out like the rolled display concept to stretch the sceen. So you'd start with a 5" galaxy S4 like device then expand it to be an 8 or 10 inch tablet.
However, I think it will be at least another year before we see this tech in any consumer products, other than maybe a wrap around display (which I don't like, phones need a little bezel).