I have both a level 70 rogue and feral druid. From a pure pvp perspective, the rogue is so much easier. The class is very forgiving - multiple ways to control the engagement, multiple abilities to "reset" the battle or escape and drop combat. If winning = fun, I would definitely recommend going with a rogue for arenas. Going by your title of "Exclusively Cat vs. Rogue", I would say rogue hands down...no contest. I find myself a free kill for any warrior, rogue, and bear druid if I stay in cat form.
With that said, I actually enjoy my feral druid more in BG's since the battle is chaotic and somewhat unorganized. The ability to track humanoids is very nice and I can move from node to node fairly quick (especially if you have the set bonus from PVP gear). I may get flamed for this (as my rogue is not very well-geared), but it just seems like the initial burst from a pounce/mangle/shred/shred combo is higher that what I can achieve with the rogue. Of course if the enemy does not die or still has quite a bit of life after the initial burst, the difficulty level is greatly amplified.