First is sound quality. If you don’t like the first watt, you won’t like more of them. That’s not my quote, but I really liked it.
Second is synergistic. It has to work well in my system (with my other components), not someone else’s, like the dealer’s…
Third is power. More is always better.
Fourth is aesthetics. It’s got to look good and have a high WAF.
Fifth is price. I have to be able to afford it as I don’t want a new wife.
Sixth is new vs used. I prefer new, but usually end up with well cared-for used. (See Fifth as I get a better bang for my buck).
YMMV (your mileage may vary)…