In a war between Oceania and Draka, it would be the Draka all the way. They have far superior technology (space travel, genetically engineered super-soldiers and war beasts, viruses that make you go mad), a more efficient system of economics (yes I know they have slavery and industrialization, but they are NOT constantly wasting resources on a pointless war like Oceania was), a government that actually pays attention to outside problems, and a competent, trained military that is not just a bunch of ignorant hyped-up nationalists. And that's REALLY where Oceania fails: they have all the resources they need to wipe out their supposed enemies, including nukes. But instead they send soldiers to die in the jungles and deserts for little if any gain, all to keep the system going forever, with no change or advancement whatsoever. The Draka actually do advance, and they seek to destroy their enemies in the most efficient manner possible.
As for whose more evil I would side RELUCTANTLY with the Draka. Mind you this is like comparing Stalin to Hitler, or Castro to Mao, or Saddam Hussein to Pol Pot. All options are absolutely terrible but there are SOME differences. Yes they are slavers, and yes they are evil for being so. But Oceania is really no different. They torture people into believing lies as truth. They manipulate people into holding a constant state of cognitive dissonance, where they hold contradictory views without ever seeing the conflict. Their minds are so broken that they rely entirely on the Party to determine what reality is. Is this REALLY different from enslavement? I would say not, so we can't use this to determine which is more evil.
Instead, lets look at how they treated their enslaved classes: the Proles for Oceania and the serfs for Drakia. Both are heavily controlled and terrorized by their respective ruling elites, but the Draka actually maintain a higher quality of life for their serfs compared to the Party and the Proles. Serfs are not constantly hungry. They can carry on love affairs without fear of their owner's wrath. And they have SOME chances of advancement. But let's NOT kid ourselves. This is slavery we are dealing with. And no matter how comfortable or how lenient or generous it may be it is still slavery. But we are comparing two evil authoritarian regimes so it's sort of like asking which one sucks the least.