[name_m]Leo[/name_m] is the ultimate boy name to me. It’s simple, strong, international, and full of energy and character. I really love it.
Its popularity was what put us off from using it eventually, it was Top 10 here when our children were born but we discussed it each time because it’s just such a great name anyway. It still feels fresh, lively and distinctive to me.
I too prefer [name_m]Leo[/name_m] to [name_m]Leon[/name_m], but I also like [name_u]Theo[/name_u] and especially [name_u]Luca[/name_u] from your list. Those are also pretty popular where I am though, so [name_m]Leo[/name_m] still wins out for me.
[name_u]Nico[/name_u] and [name_m]Milo[/name_m] are fantastic suggestions, and I’ll add Remy, [name_u]Asa[/name_u] and [name_m]Ivo[/name_m] for a few more unusual ideas. All sound good with [name_m]Alexander[/name_m] in the middle, which honours your Greek heritage.
But really, I don’t think you can go wrong with the amazing [name_m]Leo[/name_m] [name_m]Alexander[/name_m]