Depends largely on your dish/motor type. If you have a BUD, probably best to slave the DVB and use the analog to move the dish and select polarity. With a DiSEqC H-H motor and dish using a voltage-switched LNBF, the DVB should be master and the analog slave.
Of course there are grey areas, such as a BUD using newer, voltage switching LNBs or the use of a VBOX II, in which cases you might want to make the DVB master on a BUD.