Like Paul says, it really comes down to what you are designing.
For the most part, I prioritize wall thickness over infill, as it normally yields a stronger part.
Some things like fin cans, I'll create the model so the actual can is 1.5 mm thick, or 3 full walls. However, I'll design my fins to be 3 mm thick at the root. Settings for perimeter count will be set to a really high number that results in the fin being nearly 100% plastic due to these settings. This results in a much stronger fin than relying on infill percentage. I do the same thing with nosecones, and many other parts.