Hard to compare as they both have their strengths. Stirling has outrageous feet and will skin players for fun. Watch any Stranraer highlights towards the end of last season (Dunfermline 4-1, Livingston 5-2, Ayr playoff finals) - was as good as I've seen him.
Would argue that you're getting a player in the peak of his abilities, whereas Gibson's best days are behind him, although he's a standout at League One level and still deadly from a set piece.