The approach I developed over the last fifty years is to begin by assessing highly reviewed and regarded main stream products. These companies have been in existence for decades and are still top brands because of technological innovation and refinement over decades. Highly reviewed should include reviews from Stereophile, The Absolute Sound and HiFi+. These are the best and most respected journals. With professional reviewers you are more likely to get reviews that assess all aspects of the sound qualities and not just a few and to have the reviewer devulge associated equipment and personal values. Over time you will learn about more attributes and choosing well will let you discover new strengths in your purchase instead of finding weaknesses that you did not know about.
Used can be a great way to buy into much better quality and sounding equipment.
You need to think first about tube vs solid state… although some solid state, like the Pass XA series are very warm and tube like and visa versa Rogue.
Brands you should consider first and foremost are Pass (solid state) and Audio Research (tubed). Others, solid state: MacIntosh (tubed or solid state, heavy with midrange and bass… light on detail, look cool), Luxman (heavy on treble and bass… so detailed ( shy on midrange a consequently not musical), Krell (warm) Tubed: Conrad Johnson, VAC, Cary (really warm and musical).
Obviously there are others. Also lower tier NAD and Rotel.
I would read a lot and audition a couple key brands. They have house sounds… so in general they have the same kind of sound with gradual improvements over time… so listening to a current MacIntosh and Pass will give you a good idea of what you are in for with the brand.