DVD+R vs DVD-R (chapter marks)
 

from e-mail...

The physical media has no bearing over the placement of chapters. That is an authoring issue.

From the sound of it, you're using DVD recorders. The ability to place chapters is determined by the equipment, not the disc. And it's not even the same from DVD recorder to DVD recorder, the authoring abilities can vary greatly. At least one of my DVD recorders accepts both DVD+R and DVD-R, and the editing and chaptering abilities are identical on either disc.

Aside from chapter marks, is there any value to going with + over -, or vice versa? How about for CDs?

CD only has CD-R and CD-RW, there is no CD+R or CD+RW.

The reason to choose DVD-R over DVD+R is because more machines will read and accept DVD-R, especially older DVD players. In many cases, it's more about the disc quality, and not the blank formatting. A Verbatim DVD+R will be a better choice over a Princo DVD-R, for example.