[Squirrelloid]

The more important considerations with luck vs. misfortune are:

unlocked events:
-Can you handle barb and knight attacks with your PD? How much PD? (Only happens under misfortune - see Edi's thread about unlocked events).
-Do you want access to the events unlocked by high luck (or Luck AND other scale you're taking)

Gem Income:
luck will get you more gems, and more variety of gems, than not having luck will. (Especially when combined with magic scales). This can be important for diversification or just funding a summon-based strategy. While unpredictable, more gems is more gems.

Heroes:
There is a 3% chance per turn of getting a hero +-1% per point of luck/misfortune (as appropriate). So Luck 3 has a 6% chance of a hero per turn, which is something like a 50% chance of seeing at least one hero by the end of year 1. Note that each point of misfortune is actually worse for your cumulative chances at a hero than each point of luck is an improvement. (The most obvious being going from 1->0% chance from Mf2->3, but Mf1->2 halves your chances at a hero every turn, whereas 0->Mf1 only decreases it by a third). Depending on your nation, you may or may not care. (Some nations have good heroes, others don't. Some nations can get magic diversity via heroes).