As far as nutritional value, I honestly don't know. Rats have more meat, so your snake will grow a bit faster then it would being on mice.

As far as the pros and cons, hmm...
Cons: Rats cost more? They bite a crapload harder then a mouse, so I recommend feeding F/T.

Pros: Rats have more meat, they get a lot bigger then mice, so if you will have a larger constrictor, best to get them started on rats ASAP.

I'm sure they are other pros/cons, but those are what come to mind off the top of my head.