Video quality is determined by the encoder you use and to a lessor extend by the bitrate. The actual "burning" of the disk is a mechanical process controlled by the software and there is little difference what application you use to accomplish that.

If you use DVDA, you got to have Vegas which has one of the better encoders you can get outside a hardware encoder. All the decent ones cost many thousands of dollars, so I'm assuming that's out of range for most of us.

While some for sure will disagree, the DEFAULT settings are best to use 99% of the time. Period. The only real exception would be to increase bitrate if you have some very fine detail and/or fast action scenes and drop bitrate if you need to squeeze a LITTLE more on the disc.

People that say bump up the bitrate or try to get 10 GB on a single one sided disc are just hurting themselves and likely creating problems. If you encode with too high a bitrate then many DVD players can stumple trying to keep up. If you encode too low, then your project may end up looking like crap and you may as well have burned a CD.

DVD is suppose to be about QUALITY. Did I mention if you want good video quality leave the settings alone. I've burned hundreds and hundreds of DVD's using Vegas and DVD-A and Nero and yes even a few with Roxio's stuff and I can count on one hand the number of times I needed to fiddle with the bitrate. Don't mess with it. There's no need to.