Maxwell - solid classic; doesn't stand out but to me is a name that would wear well for a boy or a man
Maverick -- trendy/cute but doesn't age as well as Maxwell, IMO
Arlo -- I have a soft spot for this name because of Arlo Guthrie, but I would probably use it as a middle maybe
Phoenix -- I like this, but same reaction as Maverick. Maybe as a middle?
Silas - solid, strong name
Theodore (nn Theo) - a classic, with cute nickname possibilities for baby or kids (I also like Teddy as a nn), but something that they can also grow into
I guess my personal favorites are Maxwell and Theodore--I like classic names that have cute nickname possibilities, but are things they can grow into and will suit a grown man as well.
To get the best of both worlds, you could use them as combos...
Maxwell Phoenix
Theodore Maverick
Silas Arlo