The most important piece of advice I can give is that if you get a Dyson, learn how to take it apart and clean it and put it back together. There are youtube videos that are golden.
My first Dyson (DC25) lasted just shy of a decade, and now I'm on #2 (an Animal). When it seems like suction is decreasing, it's usually because there is dog hair or a dirt clod lodged somewhere in the machine. Or the filters need to be cleaned. If you keep the filters clean and understand how to take apart the head assembly, those suckers (ha... haha... sorry) do a good job. My husband made the outrageously stupid decision to suck up a winter's worth of crumbled creosote (when I wasn't home), and I thought my beloved vacuum was totally trashed..... When they overheat, they shut off. I took it apart, cleaned it, put it back together, and it's great again.
The volume of mud, wood ash, and animal hair and dander in our house is pretty gross. I killed a lot of vacuums that could not be taken apart and cleaned - once they're dead, they're junk. So for me, this works. The only other machine I like equally as well is a 30+ year old tank of a Kirby, but my mother is unwilling to part with it, alas.