I don't own a Vitamix but I can't imagine that it would be any better at smoothies than a TM. Thermie has some serious stength!
The TM does the most amazing job of completely blending up all the fibres etc in a smoothie, the juice is thick but smooth. I always add a handful of ice-cubes at the start to help break up the fibres of the fruit and vege. If you want the juice thinner, add a bit of water. LOVE smoothies!