As an answer to a comment from yesterday I was too sleepy to notice (Sir o Coffee I completely ghosted you there XD)
*Spoilers*
1 or 2.Lyon: Ignoring Sacred Stones gameplay which can be relatively easy, the story is quiet good. This is further bolstered by what I think is the best antagonist in the series beside Arvis who is likely tied with Lyon. His personality is that of a shy cat (similar to Olivia) but with more reason to be so. He's surrounded by people of grand worth, and incredible strength and mental fortitude and so he develops this shell. ANd then when given the chance to give his life (and subsequent ) soul to save the world at the cost of a few lives, he all but deems it neccessary. Maybe it was unconscious, but he did want it (IE where did I go wrong )he wanted to be as strong as Ephraim, to be as kind as Eirika and have his love for her returned, and he wanted to be as grand as king as his father.
The way they built his character up with flashbacks prior to physically meeting him with Ephraim made it feel all the more agonizing to see how he had truly faked the control, made it seem legitemate only to try and win, to stop a mass genocide via natural disaster. And that characterization and the way they made him feel so alive is one of the reasons he's tied for first
1 or 2.Arvis: Arvis, the mater planner who probably never lost anything in his life before Julius. His meticulous planning and tactical mind to me make his dream all the more a reality. A dream of a world with no war, where he would rule without conflict. A grand dream in itself, but opposed to other believers in the dream he could see that with enemies or rivals it would come down to only moments of peace and so he took the first step into a war for intended peace. His character reminds me alot of Lelouch (Code Geass if you haven't seen it) but this one does it slightly better.
3: Grima: Though this may seem weird just hear me out. You have a dragon/homunculus thing made from human tissue, a mix of other alchemical proccesses and divine dragon blood either gained from Naga's corpse itself (though Nagi lives so I'm perplexed by that idea), or from Julia's descendants (Genealogy and Archanea/Awakening happen in the same universe). Furthermore, with Valentia and the fact that, from lore itself, Grima seemingly shattered the dragon's table and killed everything in sight including the other earth dragons, he gains this ambiance of truly menacing power with nearly infinite patience and a tactical mind that could potentially rival that of Arvis, having waited for the weakest of the human kings and his perfect successor, his heart. He may not have had the perfect characterization in Awakening, but with Valentia and Heroes adding layers to him, I can't help but find myself enjoying his character more. M!Grima shows how humans adored him but took him for granted, and how humanities personality made him putrid inside. Furthermore F!Grima sees humans as semi-vicarious beasts (if you've heard the song Vicarious you can kinda tell what I mean in more detail). The complexity added makes him feel complete, and potentially better than what I expected.
Bonus Round:
Sephiran and Zelgius
Both of these bois almost made it to the top, but I can't help but feel that Zelgius could have had some better characterization. A reason to kill Greil other than just why not, and a few other discrepancies here and there that don't matter much in the grand scale. And Sephiran, his story is a curious one, losing his powers and watching humanity enter it's always continuous spiral, choosing to try and summon the goddess anew because he seems them spiraling once more. It's a good story, but it lacks the grand dreams and personalities of Arvis and Lyon and the masterful (and finally) complete story for Grima in my opinion.
Do let me know who you like most (or how you disagree) FE antagonists outside of favorite characters are normally the best type of chats in the community cause you can see the spectrum of character preferences.