Daemonhunters: Suprisingly enough I have had little trouble against DH. They usually pummel my daemon prince, and maybe my bloodletters, but not until they get into close combat. But by then the berserkers rip them apart. Daemon Hosts are a bugger, but they usually don't get their points worth in my experience.
Dark Eldar: If wyches get good rolls consistently they can stomp them to dust, if a talisman goes the wrong way, they'll be eating dust.
Eldar: Banshees rip apart twice their number of berserkers or a daemon prince in no time. Them, plus farseers and warlocks are a huge problem to Khorne. I have had little problem with their shooting side, surprisingly.
Imperial Guard: With good squad spacing a guard player had better score a huge number of hits. Basically they have a choice to shoot big things or berserkers. If either get through they're stuffed.
Necrons: Good monolith placement can spell doom for a Khorne player. In smaller games they're not too bad. With one they can draw so many squads, and then they just get shot to pieces. If the monolith doesn't draw them, they're about the same as IG.
Orks: I have never beaten Orks. I've come close, but not beaten them. Just too many damn units. Though I have a feeling without my awful luck in those games (defiler killing 5 berserkers in my flanking squad, my DP not going down to shoota boy fire) I could have probably won. But it would still have been damn close. Down to one unit each, I'd say.
Space Marines: There's just too much variety to generalise, but I think they're about the same as Eldar with a beefy CC HQ or with huge amounts of heavy weapons.
Tau: I just have not had any problems with Tau. Their zippy battlesuits are an annoyance, but a small one.
Tyranids: The few games I've played against them I won. I came close to losing when he drew my berserkers into his genestealers, but I still won through in the end. I have a feeling that was pure luck and could easily change. It was almost as close as Orks.
Witch Hunters: Penitent Engines just look so damn cool. Besides that, it's a mix of IG and Space Marines.
So in the end, Orks and Tyranids probably have the best chance with Necrons and Eldar doing fairly well with clever tactics. But everyone has a damn good chance of beating Khorne. If you get lucky and knock out a squad of berserkers with few casualties, that's a huge blow that could spell the doom of a Khorne player. Out of everyone, I think Witch Hunters probably have the least chance of beating Khorne, but they're not that far behind everyone else.
Now, other Chaos:
Emperor's Children: Sonic Blasters are sick verses Khorne. The squads are so much cheaper than khorne, so each berserker squad is probably taking 16 hits on average. And they're also great in CC. Daemonettes rip up berserkers just as well as bloodletters. If they get charged, though, Khorne will win. I'd say it comes down to who is charging who.
Death Guard: An extra toughness would be annoying were it not for Chain Axes.
Thousand Sons: I have no experience playing them. Extra wounds are a bugger to Khorne, and they've got some nasty tricks up their sleeves.
Alpha Legion: If they can outspeed Berserkers, yes, but it's a hit and miss affair.
Night Lords: Infiltrate could be helpful or a hinderance. Is it really worth putting your squads any closer to the berserkers?
Iron Warriors: Same as tooled-up space marines. I can see them pulling some nasty tricks on Khorne, as long as they don't get charged.
World Bearers: Daemons are a little too expensive to be that useful against Berserkers. And a bit too unreliable. But then I haven't played against a World Bearer.
Black Guard: Can get a lot of good stuff against Khorne in. I'd say a balanced force has the best chance. Bikes, Defilers, CSMs and a nasty Prince, and that's one troubling force for Khorne.
All in all, I'd say Slaanesh and Black Guard probably have the best chance against Khorne. Slaanesh (quite in line with fluff) is probably the best army in the game to take on Khorne. Shoot him half to death then charge the other half. So I'd go Slaanesh, Orks and Tyranids as top 3.
