Are we talking animations or designs?
Animation-wise, Berwick Saga is top dog IMO, followed closely by Tear RIng Saga. (If you haven't played either of those, you should!) With regard to Fire Emblems specifically, I think the GBA & SNES entries are the best, each having pros and cons. The continuous battlefields of the SNES are more immersive, but the flashier animations of the GBA are very endearing.
Character design-wise, Shadows of Valentia was the best of the modern games, but I greatly prefer Three Houses to Awakening/Fates. Three Houses' lords in particular are all top tier designs. (Three Houses also has some absolutely stand-out animations -- e.g. Edelgard's post-skip shield toss, harkening back to GBA's style -- but they're rather rare.)