Sorry if this has already been answered. I am new. Is it better to put it in DVD9 mode even if you are not using double layer discs. I see that the quality is always at 100%.

Hi marstc09 and welcome to cdfreaks.

In a word, no.
When you choose dvd9 as the "target size", you are in fact choosing a DL disc as the target, that's why it says 100%.
100% means no compression.
If you were to try to place a large file movie, say 8 GB or so, onto a SL disc and choose dvd9, the burn will fail. The default target size for a dvd5 = 4300MB(. You can increase this to about 4470 MB.)
Any movie file larger than this when dvd9 is chosen, will fail. Actually, the application should prompt you when the incorrect target is chosen.

Sorry for the short explanation, but I'm headed out the door.

Hope this helps.

Welcome to the forum. Don't think I'd do that. It tells DVDFab to expect a DL disc, and finding a SL instead will have unpredictable results, the best of which is a box popping up asking for a DVD9 to be inserted. DVDFab's compression works well with most movies down to 70% or so, even lower in some cases. If you want to keep the quality number up, use Customize mode and unselect some of the audio streams and disc extras. Select DVD9 only for burning one or if you want to write an uncompressed file to your HDD.

/EDIT/Sorry, Tom. Slow typing+wordy post=two replies for lucky marstc09.

Boy, you can't be any slower than yours truly...
Besides, like you said, two replies (or more) is a good thing...