Burn DVD on the fly? Or create ISO then burn DVD from HDD?

Hey,

Quick question. I have a DVDRW drive, and a DVD-ROM drive. Should I put the DVD into my 2nd drive and burn it on the fly? From DVD to DVD-R? Or should I copy the DVD onto my hard drive, make an ISO, then burn it off my hard drive?

I heard copying a DVD on the fly can be dangerous, but then again, it takes forever to make an ISO, then burn the ISO. =/

Anything I should know about burning DVD's on the fly?

I think that most copy programs will create a temporary image anyway.