Well, first I eliminate any types of bikes that are simply outside of my intended usage. Tri bikes, Crit bikes, Freeride/Downhill bikes that can't be pedaled uphill, Dirt Jump bikes, and so on.
That basically leaves me a range of bicycles that range from Cyclocross to Enduro, although that's kind of pushing the limits, and honestly what I really need is probably something ranging from an XC bike to a bike-packing bike. Monstercross would be a likely contender.
Then I eliminate anything that costs more than I can afford/justify at the upper end, and anything that's simply crap at the lower end.
From the remaining choices, I just buy what makes me smile. This time around it was a rigid steel single-speed 29er- the 2020 Kona Unit: