Hi Omar,
For the best flight experience, using a Windows PC is probably your best bet. Great graphics cards and high end set ups are a lot cheaper than getting an equivalent on a Mac machine. This means you'll most likely see higher FPS with higher rendering settings on a desktop PC. Windows isn't very efficient when it uses the hard drive though, so load times on Windows machines will be a bit higher.
X-Plane is (somewhat notoriously) developed primarily on Macs though because it's a more developer friendly environment, not necessarily because it runs X-Plane better.