My wife and I have a Vitamix 5000, same as the current 5200 model w/out rubber on the control knobs and a slightly different lid design. We received it free from a family member. Were we to buy it at retail price I would have probably balked at the price but knowing what we know now I would absolutely make it a priority to get.
We have used it literally every single day since we got it this spring. Every morning we make a fruit smoothie with a host of fresh and frozen fruits and vegetables. We often add fresh spinach which will make it turn green but it does not taste like spinach at all. The thing is incredible for soups (can boil it over time from just friction heat), sauces, ice-cream, etc.
Bottom line, both the Vitamix and Blendtec blenders are commercial-grade units with very powerful motors (11.5 amp and 13 amp respectively. I consider it as having a "boat motor.") Both have their fans and there are some advantages to each. The Vitamix has more manual control (flip dials and variable speed dial) and the Blendtec is pre-programmed push-buttom control. The Vitamix has a multi-part lid with a tamper to push the food around when it, like all blenders inevitably cavitates with an air pocket. The Blendtec has a more square jar with a different blade design that, as I understand it, pushes the food more up and out versus down in the whirlpool. While the Blendtec design may cavitate less and doesn't have or need a tamper as much, it can struggle maybe a little more with some applications which really can use the tamper. The Vitamix can be set and will run about forever at that speed unless you somehow overheat the motor and the Blendtec has settings which will shut down at the end of the cycle. The Vitamix is a taller unit/base and the Blendtec is shorter. The Vitamix jar is primarily designed for "wet" use while and the Blendtec jar can grind grains as well. I think that the Vitamix scores a little better on duability, but that's just from what I read but both are solid units.
If you are considering one I would check their respective websites to see when they have a show at a place like Costco. The best prices are at shows like Costco, Costco has a great return policy and you'll get free samples with the opportunity to ask any/all questions. Please feel free to ask me any questions about a Vitamix, how we use it, etc.