I started out ripping everything to FLAC but when I couldn’t find a car stereo with the features I wanted that also played FLAC I switched to WMA Lossless. I’ve never had any problem using Media Monkey to assign metadata to any file FLAC or otherwise for it’s own internal use. For exporting to the car the same as you “Artist, Album, Title and the like are all that I use.
I do have a lot of stuff come up w/o database entries or album art but I seldom care about the art. Even if the database doesn’t find the tracks I can still rip it based on Artist, Album myself.
The features I really like the most are the things in MM like “Mood” and “Tempo.” Though I have to tag those myself they’re nice for later random playback when I want a better mix than just selecting a “Genre.” I highly doubt I’d be such a fan of ripping if I didn’t have MM to play with.
