Aspect ratio just refers to the ratio of the dimensions of the video. If you don't want to distort the video then don't change the aspect ratio. If the video's aspect ratio doesn't match the screen dimensions of your device and you want the video to be full screen then you'll need to adjust the resolution/aspect ratio. There's no universal "best". You need to clearly define what you're looking to achieve.I've been playing around with Handbrake to convert some avi's to mp4's. Anyone have a handle on what settings work best? Aspect ratio etc....?