I think I may agree with Sweeny, but hell, I zoned out twice trying to read his post. Good grief!
Mike is right, the Shark vac is the best one out there, but only because the Dyson takes so much heat from the mills regarding voiding warranties. The Shark vacuums just as well as the Dyson, and if it did not have such a small head and dust cup on it I would prefer it over the Dyson. They make larger Shark vacuums, but they are more than the price Mikey quoted. I bought my wife a Shark several months ago and I use it when I clean our house carpets. We have two dogs (thanks to Lizza) and they both are quite hairy. I have to empty that darn dust cup so often that I fell like it takes me twice as long to vacuum as it would with my Dyson.
So, if you have $500 to spend, get a Dyson.
If you only want to spend $150, get a Shark.