It really depends on your footage. If you have a 720p video, render in 720p. If you have a 1080p video, then render in 1080p. If you have a lower resolution video but render in 1080p, the pixels will blur together in an effort to fit the amount of pixels. I would recommend using the mp4 codec, and editing it to make sure the framerate is 29.97, or something like that. If it works for you, select render with OpenGL or CUDA option as that will significantly decrease render times. The main thing is, your options have to match your footage, otherwise distortions will appear.