My sister-in-law made me rethink using margarine for everything

So my SIL from Columbus visited last week and watched me grab margarine for my sugar cookies without blinking. She asked why I never use butter and I laughed it off, but then she asked if I'd actually ever done a side by side test. I hadn't. That afternoon we baked two batches using the exact same recipe, one with margarine, one with butter, and the texture difference was unreal. The butter batch spread less and had this crisp edge I never got before. Now I'm wondering if I've been doing it wrong for 8 years, or if it's just a preference thing. Has anyone else switched after a comparison like that and never gone back?