I've used both and both work great. I think the Vari-zoom has a longer cord on it compared to the springy cord of the bogen. That being said. I use the bogen. They both are quality as far as I am concerned. I'd get the cheaper of the two.
I just picked up a Varizoom Rock LE at a very good price and like it a lot. The Bogen is very similar, but the Rock has a few more features like the Autofocus button and frame advance. When it comes down to it, they are both very good.
Also - forgot to mention. If you are taking them off and on often - the Bogen comes off in a second, and you won't loose the friggen adjustment nuts like we do constantly!