Optimal Aspect Ratio For Pictures on Home Page?

[fasteddy]

I have custom backgrounds enabled for Pictures in the home page (just points to a recent folder of random pics), but as they have different aspect ratios, they end up distorted on the Home page, which is less than impressive when I'm showing off my htpc to friends. What is the optimal aspect ratio to crop my pictures to?

[Edit: I'm using PM3.HD on a 1080p setup]

[Jezz_X]

16x9 is optimal eg: 1280x720 ot 1920x1080 makes them fit into the space fine