I started designing icons in Adobe Illustrator. Working as UI/ UX designer in Sketch I needed to quickly design few small icons for the website and this is how I found Sketch as a great alternative for icon design.
I agree that Adobe was made for icons and illustration, but for me, Sketch is much simpler and easier for pixel-perfect icon design. In rare cases, If I can't do something in it, I use Adobe. Sometimes I combine all these tools.
I guess it depends what suits you most. For me it's Sketch 🤷♀️