[MinaciousGrace]

fon is generally for characters that are naturally tanky and depend on mobility to function aka singed skarner etc

irelia would probably fit in here better

bveil is for characters that arent naturally tanky but need a bit of a boost to avoid getting instagibbed by an ap caster combo

last i heard (read: 3 months ago) bveil was falling out of favor since if you were positioned incorrectly it didn't matter whether or not you had it you died anyway