Warlord. Instant no brainer. It would be an inarguable olive branch to a community that has, more than once, felt pretty damn snubbed by 5e, and would have various other benefits as well.
I agree with
@Mistwell that Swordmage is also a reasonable choice, given the game has tried
so many times to do it by half-measures with other classes, but knowing 5e it would just be another half- to full-caster, and I'm pretty against that. A Warlord would be a rare instance of adding a class that
isn't a spellcaster (absent the perfectly valid possibility of a spell-focused subclass), when 5e is
suffused with classes that use spells. Even with a broad definition of "not a spellcaster", 5e only has four classes that don't cast spells (Barbarian, Fighter, Monk, Rogue)--it'd be nice to at least
try to keep that to "around a third of classes aren't spellcasters".