Horizon you need stamina to read....Since I got vol 4 when it was released I'm only like 2/3 through to be honest since I don't have enough time to really blast through it in one shot.
Zetsuen it depends how Bones will handle it. And whether you like long winding, complex plots or not. The whole thing is really one "fate has set it up this way" "breaking fate's laws" kind of story. Personally I enjoy it but many dropped the manga because of that.
I can't stand Mushroom and SAO mainly because they're not good enough to warrant such a rabidly fucked up fanbase.