性价比? 这个在 英语 (美国) 里怎么说？

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[consumer/engineering]
"price-performance ratio" is probably the most direct translation of 性价比, often applied to devices/tools (audio, cars, digital, phones, power, etc.)
"This phone has a much better price-performance ratio than the flagship model."

As @SeaPebbles already mentioned, "bang for [the/your] buck" is very colloquial but common and entirely appropriate.
"These speakers give you great bang for your buck. For even more bang for the buck, you might consider..."

[business/economics/finance]
"cost-benefit analysis"; "value"
"After a careful cost-benefit analysis, the local government decided to re-open businesses but require everyone to wear face masks."

Especially because the situations you have in mind are likely to involve qualities that are not clearly measurable, I'd stay away from terms like "price-performance ratio" or "ROI (return on investment)"!

[general]
"pros/cons"; "advantages/disadvantages"; "benefits/costs"; "perks/pitfalls"; "[the] upside/[the] downside"
"Hermione realized that the pros of graduating early from Hogwarts were outweighed by the cons, so she decided to stay at the school for one more year."

"This situation has no upside; you should get out of it as soon as you can!"

"The established company offered me a better package, including a higher salary, health insurance, and other perks, but the prospect of being part of the team that will build a new company from the ground up was too exciting to pass up."