After trying these for awhile, I have to agree that the Jazango one is by far the best. Never had a busy signal or even a wait for a line on it yet. Plus, it seems to connect to all the countries it says it does, where I've had problems with some Canadian area codes and some country codes on the Futurephone ones.
Also, these make a nice divert for toll free numbers that blocks your ANI pretty good. You dial the Jazango number, then at the prompt dial 011-31-20-3987567 and you get a dialtone. At the dialtone, dial * followed by the toll free number, like *1-800-444-4444. The ANAC says your number is 702-403-1000
Nothing like bouncing your call from Cass Lake, Minnesota to the Netherlands back to North America and end up showing a Las Vegas number on someone's ANI.