Only certain alloys are used for bicycle frames besides other materials like carbon fibres (at least for the mass market). I often stumble over aluminium alloy 6061 and 7005 (and I think I saw 8004 once). It doesn't seem feasible to say that one is better than the other because they have different criteria like density/weight and break resistance. Increasing those criteria towards ideal values for biking (less weight, more break resistance) seems adverse, i.e. engineers have to make a decision between the material trade-offs when selecting it and I as buyer need to recognize their intention to make the right choice. There might be criteria which have non-obvious impact like better processing of a more dense alloy allows to construct thinner frames so that maybe an alloy with less density systematically results in a more heavy bike.
I'm excluding the price from the list of criteria to make the question more answerable.
I'm happy with a reasonable simplification like x always allows to build thinner frames than y while providing the same stability and is thus always light and preferable because of a. Or a sorting of relevance of criteria and a description of trade-offs between them, e.g. it seems that certain alloys bend before they break whereas others break immediately, but then under heavier impact only. I don't even know which one I want (I assume I can't bend the frame back after a crash, so is it a question of security? Can the broken frame be welded back together? Those a just example questions…)
I'm not interested in the criteria the manufacturer uses to select the material for the frame, like weldability, price during a certain period of economic up and down, etc, unless it has impact on the quality of the bike.
I hope you don't recognize this as primarily opinion based. I'm looking for a listing of criteria with relevance to using the bike of which the frame is a part - besides a ton of other criteria which is important in engineering, but irrelevant for biking (like the melting point).
There are certain clues, like "used primarily for less expensive bicycle frames" found in a Wikipedia article on the 7005 alloy, and of course a ton of unverified information in horrifying forums.
I can add an advertisement-like reference for the use of the alloy for different bike frames.