Scandium is an aluminium alloy and essentially aluminum.
All alloys aside, steel is going to be the more comfortable and forgiving ride out of the duo.
I've ridden a Columbus spirit tubed bike and the tube set is designed for a stiffer more solid feeling ride than traditional steel tubing all the while still maintaining steel's shock absorbency.
I can't speak for scandium however due to its uncommonness but it's 0.1-0.5% alloy w/ aluminium.