My usual method:

Slide CD in

Tell it to "Open Finder" (perhaps counterintuitive here)

Go to the finder window, on the left you'll see "Untitled CD"

Click on "Untitiled CD" and drag-and-drop stuff into it.

Click the nuclear radiation sybol next to "Untitled CD". At this point it should let you select the burn speed.

All that being said, I've used disk utility to burn iso's plenty of times and never had a problem with it.

Matthew