yum vs. up2date

[Mike WItt]

I've been experimenting with yum and up2date. They both appear to
have their merits. I've got a couple of additional questions.

(1) Is it "safe" to use both yum and up2date? It *appears* that
    one recognizes changes that were made by the other. Is this
    always the case? Or can you get in trouble if you don't stick
    to one or the other?

(2) What is the best way to go about finding the "right" repositories
    to use? Both in terms of getting the "correct" updates, and also
    in terms of not generating undue traffic?