My feet are US men's size 13 (EU size 48) with an average (D) width. I've ordered maybe 35 pairs of leather and plastic boots to try over the last 20 years in search of boots with a perfect fit for my feet. I typically wear new boots around my house for 1-10 hours to test fit and comfort. For a long time I found less than 10% of boots I tried on fit correctly. The key was finding which manufacturer has a fit that matches my feet well--namely La Sportive and Scarpa. I can't wear boots made by other companies. I find the fit of different Scarpa boot consistently the same. With La Sportiva, the fit of different boots varies quite a bit. After 20 years, I finally found a boot that fits my feet perfectly--the La Sportiva Nepal EVO GTX.
I've actually purchased the the following boots and used them extensively.
La Sportiva Trango S (2 pairs, slightly narrow for me but flexible enough to fit)
La Sportiva Trango Alp (identical in fit to the Trango S but sturdier and more waterproof, slightly narrower than the EVO - I use these for 4-season hiking)
La Sportiva Trango Extreme (close fit to Trango S)
La Sportiva Nepal EVO (only boot that is perfect for climbing and winter hiking)
Scarpa Cumbre (longer and slightly narrower fit than La Sportivas, wider toe box)
Scarpa Triolet (similar fit to Trango S but curvature at front is angle differently)
Lowa Denali (2 pairs, a bit too narrow at the ball of the foot)
Asolo 8000 (2 pairs, a little narrow at the ball of the foot)
Millet Everest (US men's size 15, unique roomy fit, use in Alaska)
