These skills are very similar as both reduce movement speed, damage all in front of you (up to five with SS), the range is similar and the cost about the same for base damage done though SS cost receives a 10% reduction with the Intimidate skill making it less cost per damage than AS. If you have access to Dolems then SS is available before AS. I am aware that AS damages each target equally while SS does 1/2x, 1x/ 1/2x (three target example).
It seems to me that SS fires faster than AS but this may be just perception.
I prefer SS. Can anyone make an argument for Arrow Spray as the preferred of the two?