i would be inclined to say there is not a difference.
I tend to use field1,field2 for loops.
mostly because if i am taking 7 of 10 fields from 50 entries in the DB
it should save time.
i'm not sure if there are any security issues with * and used data.
that is my 2 cents .. feel free to give me change if you want.
hope that helps.
chris