Apple Motion JPEG B, with the MPEG Streamclip quality slider set to 100% (lossless), is perhaps your best bet for an intermediate codec. This is true for nearly all video destined for web or DVD. It's pretty fast and offers good compression, while maintaining lossless quality in most workflows (including the one you mentioned). It also comes with QuickTime, so it's "free". You'll need a decent amount of free disk space of course.
thank you for the info. I have the streamclip converter and it is really nice..(can't believe it's free?)..did a little bit of research on jpeg a vs b and of course, I really didn't understand what it all meant ;(...Why do you prefer to use the b over a for editing and conversion?