In a nutshell, a little of column A and a little of column B. At this rate Selena has a better chance of being dead, than at half HP. Certain skills like Awakening have only limited usefulness due to the fact that they require the unit to be below half HP in order for it to work. On characters like Saizo, it basically guarantees that something activates (usually resulting in a OHK). I don't personally like quixotic unless it's on a unit with above average skill to begin with. If that doesn't appeal to you then take an offensive skill like Rend Heaven which has a fantastic proc rate of skill x1.5 (plus quixotic). If you took a breaker skill you can double down and take another to make yourself more defensive. This leaves you with 2 slots still available, one of these should have a sustain skill or breaker skill to offset incoming damage. Because of that I would never recommend taking quixotic without taking lethality (since this gives you an increased chance of killing your target outright) and vantage (because if you get into a tight spot this can really turn things around). Meaning that if you end up fighting an enemy that is either on the difficulty of Hard and up or player made characters, you might run into some serious issues. Quixotic increases the hit rate and skill activation of both units involved in combat. Now here's why I think it should be this way. Vengeance ( do not use if you have Sol equipped) In my opinion, here's the priority of skills based on whether or not you use quixotic.ħ.

Selena fire emblem fates