Decoupling Capacitor Loop Length vs Loop Area

When considering inductance reduction, what is considered more important? Reducing the loop length or the loop area?

Loop area is the most important consideration.

When the wires are close (forming a smaller loop area) the magnetic field on one wires tends to cancel out the magnetic field from another. That reduces loop inductance.

If you use this parallel wire calculator and mess around with values you'll get the gist.

See non-inductive windings. A long wire, looped back on itself so it presents very little area, has a very low inductance. Area, not length, is the factor that controls the inductance. The magnetic field of one wire is substantially cancelled by the other.

Image from wikipedia

Area is what is most important. Also what is inside the loop if there is something there with significant magnetic properties.