I like both, but I prefer
Rowan. I think a decent number of people might be inclined to pronounce
Roan with one syllable because of its similarity to
Joan in terms of appearance, whereas
Rowan probably won't be mispronounced as often because it's more familiar.
Rowan makes me think of berries, red hair, and foliage. I love it.
Roan makes me think of coastal
Ireland due to the film "The Secret of
Roan Inish."