My favorite is 8ballClub completely free but for some reason why back they stopped allowing players sign up not sure if this is a UK lock out or everyone.
http://www.8ballclub.com/
Out of the two you have posted I have played the free version of virtual pool and it was ok but I do own the paid version of pool nation FX the latest in there series.
http://store.steampowered.com/app/314000/
Am more then happy with it so far they is a free to play version of it also so worth a try before you buy, they seems to be a decent amount content in there and player online seems a good number I dont find it hard finding a match.