What workflow are you using? And what, exactly, is it you aren't happy with as far as quality?
Treat it like any other project: use ProResLT to edit and export. Once you're done and have exported a FCP movie, use Compressor or MPEG StreamClip to do the conversion to a YouTube-ready file.
For what it's worth, I have never had a good experience exporting via Compressor. I always export a self-contained FCP movie at current settings, then use Compressor or MPEG StreamClip after quitting FCP.
I always export with Compressor unless a plugin is glitchy. The quality of the x264 encoding almost always depends on the bitrate/frame size. On some projects I have to export 20-30 individual sequences and I couldn't imagine having to baby the computer while I exported via FCP for each one. Compressor allows me to just send everything over in a batch.