Best cordless vacuum cleaner?

Folks- some good deals out there and want to buy a cordless vacuum for my duplex apartment with lots of stairs.

Confused between shark and Dyson as of now. Dyson v12 is available at 399, Dyson V8 at 240 and shark stratos is at 280.

I want to buy Henry quick but don’t like the hassle of buying and throwing bags after few cleans. Will buy from Harvey Norman or Curry etc.