Is it better to use AirPlay to push from Mac to AppleTV, or use AppleTV to pull from a Mac?
There's no difference in quality, so it's purely a personal choice and depends on how your home network and systems are set-up.

I have a Windows PC running iTunes 24/7 and that has my entire library of music and video on it, so the Apple TV can pull whatever I want from it.

Sometimes I'll play content such as BBC iPlayer or Youtube videos from my phone, or from my laptop if I've downloaded a video I want to watch without importing it on the other system but it really makes no difference. It's just about convenience really.

The only thing that really makes a difference is network connection for the caching, wired ethernet is obviously a lot faster than WiFi.