Along which dimensions can two candidate solutions each be called "best", and what single trade-off do they all reduce to?

Different solutions win on different axes — time, money, feasibility, reputation, user value — but every axis ultimately collapses into "effort versus return" (Aufwand und Ertrag).

The same problem yields several "best" solutions depending on what you weight:

These are not independent: spend more (money, effort, time) and you usually get more durability or value, and vice versa. That is why they all reduce to one balance — effort versus return. "Best" is just the point on that curve where the return justifies the effort for your particular priorities.