Toast will burn both mpg & avi. But I think there might be some avi formats it can't burn. AVI is like QuickTime ... it is purely the outer shell ... the actual type of avi can vary greatly between different types (eg: divx, XviD, 3ivx, Matrovski, etc.)

Mpeg has less options within Toast. It can't be edited, etc. As to which is best ... well that depends on the original conversion quality of each particular file. There's no one is better than the other.

However, DVD's use mpeg2 format by the way. VCD's use mpeg1. SVCD's use mpeg2. So if it's avi then Toast will need to convert it.