Roan is far too horsey.
Ronan ... I once knew a
Rowan, very pleasant man, who named his son
Ronan - I can't remember his wife's name, but I know it had an n in it somewhere, so
Ronan was a merger and also the name of a former pupil of
Rowan's who realy impressed him.
Myself, I like trees better than Irish names, so
Rowan. But they're both good.
Rowan is perhaps easier to pronounce.