It takes my burner like 2 mins to erase a dvd-rw. lol That's using Roxio Toast, which has both quick & long erases & most decent burner programs offer this option. Quick erases simply erase the TOC (Table Of Contents) which contains all the directory information & is the very 1st thing that's burnt on any type of disk & takes up the 1st few sectors, etc. Actually TOC refers to CD's, but both TOC and DVD Structure (roughly same thing) are located in the Lead-in of a session.

I use RW's for borrowed dvd's so we can watch them at our leisure. When customising dvd's I like to use RW's to be sure layout & effects & usability appear as designed.

DVD-R's certainly are cheaper these days & a loss of a disk is not a major catastrophy. ("frisbies" lol) DVD DL's are a more tricky proposition since the layer jump point & type & direction can play a major part in both the disk's successful playback & layer jump delay time. At least this is true for custom video disks. DVD+R DL's seem to have an advantage in regards to this on the mac. Also 1st layer must be larger than the 2nd.