[@mattmanganon]Star Wars would probably be a bit more interesting, as it introduces a whole new universe for them to interact with, with new situations and species they have to deal with.

Another Star Trek ship wouldn't really be that unusual to the crew of DS9, though it could work if, say, a crew from the mirror universe came through, a race from the Delta quadrant, or maybe ancient people from their universe (say a Vulcan ship from just after First Contact).  The last wouldn't really have anything to offer in terms of military, though.