Pg is thinner, provides slightly more throat hit, does not add sweetness, and produces a thin vapor.
Vg, is thicker, sweeter, and produces clouds if vapor. Vg on its own can be rather thick and goopy - especially when cold.
I find a pg/vg mix works the best and I mix my juice at 50/50%. Many retailers sell their juice at an 80% pg / 20% Vg mixture which works great as well.
To add to the confusion, there is also peg. Peg has the characteristics of Vg in terms of vapor, but is not sweet and provides the throat hit of pg.
Hope this helps