Hi Herbert,
Usually, you make that decision based on the size of the print.
The 3800 doesn't take roll paper, so I think your largest size print might be 17 x 22; not sure, but if that is correct or close, I would use 720 ppi.
It takes longer to print but I want the best I can get.
Try a print at both settings and decide for yourself.
Many people using roll paper and making prints that run 24" x 48", will use the 360.
It takes less time. You view the print from a greater distance because of the size.

Give it a try both ways.

Fred