First off, you definitely want VBR (Variable Bit Rate). This assigns the minimum necessary bit rate for each scene, whereas CBR (Constant Bit Rate) will assign the same bit rate to all scenes regardless of content (very wasteful-big file sizes). If possible, look for an option for "2-pass VBR", to give the program a chance to analyze the video before applying the bit rate (though I'm guessing it won't be there.)