I've gone for the n+1 approach, as it seems anything that's good at stairs will be a bit rubbish elsewhere.
So: eBay FrankenKirby[1] upright: It's built like a tank[2], easily dismantled, parts are readily available, and it sucks so hard the wheels are powered in order to make it pushable by mortal humans. Beats carpets into submission, and eats wood shavings etc. without a fuss. Uses a bag, so you don't conclude your cleaning experience by sticking your head in a wheelie bin with all that lovingly HEPA-filtered dust. We finally made use of the carpet shampoo feature the other week after I regained consciousness in a pool of not-so-precious bodily fluids three steps from the bathroom. There's now a suspicious clean patch on the carpet.
Makita cordless handheld: Uses the standard 18V power tool batteries, which neatly sidesteps the crap proprietary battery issues (and means my tool batteries get more regular use, so don't degrade in storage). Built like something a tradesperson would use to suck up small quantities of plaster dust, rather than a plastic toy, and the brushless motor means the point of failure is probably going to be the membrane switch. Performance is best described as adequate, but I've been spoiled by the Kirby (which is a faff to switch to hose mode for the stairs). Is doing good service removing bedcrumbs from the vicinity of barakta while she's immobile post hip surgery. Like all bagless things, emptying it is fine if you've only sucked up sawdust or LED legs[3], but horrendous if it's standard household fluff and human hair.
Needless to say, the accessories have different pipe diameters. But even Makita can't get that right with their dust extraction outlets.
ETA: N+3 would probably be a Henry of some sort. They do one thing, which makes them unsuitable for an n=1 hoover in a house that combines long hair and carpets, but they seem to do it extremely well.
[1] Irregular reminder: Never buy a new Kirby. It's a scam. The machines are well-engineered (probably one of the best implementations of the classic bagged upright vacuum cleaner), but their sales practices are deeply unethical.
[2] I carefully bought an older model from before they started switching parts from metal to plastic.
[3] Ie. the little bits of wire, insulation and solder splatter that end up everywhere when you've been molishing prototype electronics. It's brilliant for this.