I have a Dyson and I love it. Kirbys are good but waay overpriced (never accept the salespersons first offers, you can talk them down to half.) My bf went through the training sessions to sell Kirbys and they have some really crappy sales tactics to guilt trip people into buying the vacuum.
I spent $350 on a Dyson (bought from authorized dealer on ebay) and its so much better than the cheap one I had before. I cannot believe how much hair/dust it pulls from the carpet.