I liked the idea of a button fly, and had one put on my first MTM Oxxford. While I still admire the extra craftmanship and detail that goes into handmade buttonholes as compared to a zipper, from a practial perspective a button fly is a pain in the a--. The fly also doesn't close quite as flat (great grammar!) as a zipper fly...I've gone with a zipper since then.
I collect Esquire magazines from the 1930s which is about the time zipper closures replaced the button fly. Most issues have advertisements for the zippers extoling their convenience, reliability, and improved aesthetics compared to a button fly.