I fold. I find that you get a cleaner wipe with less smearing, and by folding you actually get more on the paper than simply scrunching. Also when you fold your tp, once one side is used, you can fold it over and use the other side. You get more bang for your buck and you get done faster. I've back-tested this method over 10yrs and find this is the best way.
Hope this helps fellow wipers out there.
cm