If you want the very best encodes go from your timeline and Export to Compressor. Use CBR 7Mbps instead of any VBR preset. Even though you don’t need the room compress the audio to ac3, it will playback with less issues on a wider number of players.
When you can get the bitrate up past 6Mbps using VBR is counter productive. Using CBR also shortens the encoding time.
This does tie up FCP while encoding but you asked for the best method.
BTW, if you have any effects UNRENDER them before sending the timeline to compressor.
As stated the better the original footage/codec the better the encode but this will always give you the best with what you have.