MPEG 4 vs DV

When creating a new project there is the choice of MPEG 4 or DV.

I just opened one of each and dragged and dropped a 3 second MPEG 4 clip into each clip pane. Both took about 7 seconds to import and resulted in full dv files in the media folders. Size, not surprisingly, rose in size from about 2.8meg to 12.6meg.

So why choose mpeg4? Does it mean anything in this context?

There is a reason for my question:

I thinking of buying a new pipeline inspection camera that has an integrated recorder that stores mpeg 4 files on Compact Flash cards. I want to import the movies into imovie for editing prior to burning an SVCD for customers. If imovie ends up converting them to full dv (no matter what format I choose) in approximately 2x real time, I might as well stick with our present system that records on VHS cassttes and is imported via a canopus ADVC 110 in real time

One major advantage of going over to a digital format is that file transfer between recorder medium and computer is so quick. If I then have to wait for a lengthy conversion process at more than real time It rather looses the point.