Neither player is a number one scoring option, both are probably best suited with a pass first PG that can set them up or defer to the number 1 option.
Where I think the biggest difference between the two is that Smith is demonstrably better at rebounding, defense, and having a proven ability to play well in the playoffs. I hate to say it but those areas, to me, have always been effort and toughness stats.
I think Smith has at times "Antoine Walker" disease with his shot selection but his defense, rebounding and ability to show when it matters most makes him preferable to have on this team than Green.
But I honestly, don't want either player on this team. Trade Green but for someone better than Smith.