> Am I going to get a lower quality QT file if I export using the "Quicktime
> Movie" setting rather than using Quicktime Conversion
No -- in almost all circumstances, you'll get a higher-quality movie file. The reason the QuickTime Conversion takes longer is that it's harder to compress media to a lower format than to export it as is, verbatim. When you export verbatim, there are no calculations, no file conversions, no new codecs.
You should probably read up on codecs, file formats and so on for a better understanding of what exactly the QuickTime Conversion is doing.