“Good” glass is very important. Eye relief is important (I won’t buy a scope with less than 3.5”). But durability and precision are numero uno to me. If it doesn’t perform when needed, it’s worthless.
Price is a major consideration. For some, paying $2-3k for a scope isn’t a big deal. For others, $500 is major money. Using a basic 3-9x as a baseline, I think buy the best you can afford but decent scopes start at around $300.
If someone can only afford, say, a Savage Axis. Rather than buying the “package”, buy the rifle, save up some money and buy some good mounts and a decent scope, rather than some $100 special. Their experience will be a lot better.
What goes along with this is magnification variables. 3x (3-9x), 5x (2-10x), 8x (1-8x). Obviously the more variable range, the higher the price. But this doesn’t necessarily equate to a “better” scope.
I look for a good crisp view, with good eye relief and precise adjustments.
The durability is based on not only reputation, but your experience. It never fails that I take at least one good fall each hunt.
Some scopes have wonderful glass but lack in other areas. So far (knock on wood), Leupold have been my go to. But I have Zeiss that I like too. I had a Swarovski. Great glass but knock it against something and it would go out of zero in a heartbeat.
One criteria not originally mentioned is weight. Some of the high end scopes weigh 4 to 20 oz more than others. I can probably live with 4oz, but an extra pound? I don’t think so.