Jonny, how long is your project? Often if it's longer than 50 mins, auto programing will do all sorts of compression to fit it on a DVD. Also u/w video isn't the usual scenes that auto settings are made for. So many times the quality will suffer.
Compression is a black art where maybe 20 people in the world really know what they are doing. And those bastards are getting paid well for that alchemic knowledge.
If you have very complicated scenes involved lots of blues and little fish... it may pay to go learn a compression program instead of relying on autosettings.
A few tips:
1. Gamma correction for TVs
2. Motion detection should be a bit higher than normal
3. High bit rate as possible
Just realize as you mess with settings, the longer the render will be. I use Bitvice to output but also use compressor, even though I don't like the interface. The Apple Mpeg2 codec is much better than it was just 1 year ago!