Vacuum Cleaners Discussions

I get wrapped around the axel when it comes to making decisions involving this much $$.   My Hoover 3755 has finally pooped the sheets and I am looking for a high quality, durable replacement.     I have a fair amount of medium shag carpets, a dog who sheds a lot, lots of wood and travertine floors.

I really want the Calisto, but REALLY, REALLY don't want to spend $1k after tax on a vacuum.   I have the opportunity to pick up a Simplicity Verve for under $500 brand new, which places it very close to the price of the Titan (close enough to where the price difference is no issue).   How does the filtration compare between the 3?   I like the idea of having the larger power head which makes me lean towards either the Verve or the Calisto.  The Verve also comes with a very comprehensive set of tools.   If I REALLY have to, I will pony up for the Calisto if people here think it is worth it, or is the price I can get the Verve for a no-brainer and something I should do?   Or the Titan?   Help.