Iskander is a joy, he cares about you as more than minions (even becoming a dad figure for Waver), he has amazing charisma, he is a strategic genius who always does his research, despite that, he also is someone who has honor and is direct. He won't throw you away as easily as the aforementioned Erwin. He's honestly fun asf. Plus I want a good dad.
He's better than the rest of your choices. Heck I'd follow even his real life counterpart if I was alive back then, who did stuff like free the Egyptians from Persian prosecution and rule (by crushing them in egypt), who's apparently the son of Zeus and a descendent of Achilles both (ancestor Achilles, his mom was banged by Zeus, it's all gucci to horny Zeus). Pretty much revolutionized Egypt and gave them a golden age including creating the city that became it's capital Alexandria based on Iskander/Alexander the Great looking at a map and finding a village in a good location and pretty much making it into a great city. The people he kept there to rule (without the religious prosecution and stuff, the egyptians actually loved him) were the ancestors to Cleopatra herself. While there, did a big dick sacrifice to the gods and respected their religions and visited the Apis bull, and then went to a medium of the gods or something that said he was actually a demi god like his mother claimed he was. He did all this and was a strategic genius who studied under Aristotle (who was his private tutor lol, big dick asf), and apparently was praised by him as well, and he was like 20 years old. He went on to beat Persia and his rival Darius III, who was the king of Persia. He was considered un-killable in battle, and died relatively (like upper 20's I think) due to getting a fever, despite surviving countless battlefields.
Alexander the Great (known in the east as Iskander) is literally an anime character irl, even if you dont' believe all the greek god stuff, he still had a cooler existence than any of us will ever have, I'd follow both the irl version of him, and the Fate version of him, what a lad.