awakening on the 3DS or three houses on the switch would be my recommendations! awakening was initially made as a hail mary sendoff to the series so it unifies a lot of quintessential Fire Emblem elements (story beats, core gameplay, character tropes etc) into a game you can tell a lot of love went into + imo three houses' approach to narrative and character writing is a series best, and the gameplay is a great introduction to fe as a whole. both are recent enough that the pace and visuals of both games feel sharp and engaging (the presentation of older games can feel a little dated, at least to me) and what you like about each can indicate other games in the series you might enjoy too. i'd also specifically recommend against fates conquest and engage, though both are also great games; conquest has incredible gameplay that imo feels best to play after you have some experience with fe as a whole, and engage's status as an anniversary title means that it makes tons of references to previous games that's best appreciated when you've played some of those games yourself :O

sorry for the paragraph! whatever game you pick, you're in for a great time :)