It's personal preference. There are pros and cons to each:
PG - Better
throat hit, thinner, may irritate the mouth.
VG - Thicker, more vapor, milder on the mouth, less
throat hit
For this reason, most people prefer a mix of the two, 80PG/20VG and 50/50 are popular, but they can really be mixed in any combination to suit your tastes. Personally, 80/20 does it for me and I find 50/50 too thick.