What's wrong with Endermen farms? Spawn rates are terrible on guardian farms, true, but I've yet to see an issue with Ender grinders. Personally, I recommend blaze farms for even cave spider farms because you build around the actual spawner and are guaranteed spawns. Cave spiders spawners are nice because you can often find abandoned mineshafts with multiples spawners within 16 blocks of each other, and blaze farms because they give the highest amount of xp in the game (same as guardians, I believe).

If you make a cave spider farm, you can also use the drops to trade for emmies at the trading post.