I use FLAC because of more widespread compatibility. Mostly because that's the format my portable supports, even though I never use it on the portable. Plus it's sorta related to Ogg Vorbis, which is the format I do use on the portable. I dunno, "keeping it in the family" so to speak.
320kbps mp3 is not lossless and never will be. There are artifacts of MP3 encoding that will never be completely eliminated. If you're going to bother going that big, go FLAC or APE and be done with it.
Oggdropxpd accepts FLACs as input, it even transfers all the tag information automattically. What I do is use FLAC on my home system for listening, and oggify anything I want on my portable. That way I don't have to compromise on sound quality for my home listening, nor do I need to carry around excessivly huge (320kbps) files on my portable. I'm not sure that you can set up razorLAME or annother LAME front end to do the same thing with mp3 that oggdropxpd does with vorbis, but I would be suprised if nobody has gotten around to doing so yet.