I personally favor the Demon, for the simple reason that in such a non-juggernaut non-Lucifer situation, the GTVA will simply set up heavy-duty node blockades on the nodes they can use and fire a Meson Bomb down any unstable nodes in the system to keep the Shivans from using those. The Demon can defend itself against a node blockade, but the Ravana is out of luck against those Mjolnirs to its sides.
Also, it has been my experience that the Demon is actually more difficult to attack successfully then the Ravana. (Though neither is particularly difficult.) The Demon has all-around antifighter coverage, and generally more of it. For the purposes of this comparison we will discount the blob turrets as generally ineffective. (I say that because they aren't dangerous enough for me to memorize their placements.)
The Demon has a forward flak gun and missile battery, two missile batteries and a beam for each side amidships, a flak each for the rear left and right, and a flak for the lower stern.
The Ravana has jack-diddly to defend its front against fighter attack (which is another reason it would rapidly lose its main armament), a flak for each side amidships, another flak each for the aft sides, a beam for the lower midships, and a flak for the upper and lower stern.
The Demon would seem to come out ahead, except in terms of stern coverage.