It depends on what quality you want. You can set it for iPod resolution (320x240) or TV (640x480) and you can change the quailty for each. Both resolutions work on iPhones and ipods. Very simple app and works great!
:2cooliSquint is the easiest. MPEGStreamclip has some issues converting on its iPhone setting, but I have not updated in a while. Otherwise, it is necessary if you have a hard drive camera and need to convert MPEG videos to edit them.
I have QuickTime pro and I don't think you can even open real media files with it because it automatically opens with realplayer. So I don't think there is a way to convert the file through quicktime pro. Correct me if I'm wrong.