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Tyranids have been labeled as the overall best CQC army in the game, but is that true?
Chaos Daemons are extremly good a CQC too, are Tyranids still the best?
I have also put this question on the Chaos Daemons page, I want your opinions, explain them well please.
As for the OP question, it really depends. Obviously, one squad of 10 gaunts is not going to defeat 10 Bloodletters in close combat. However, the Tyranids have numbers. I'd say that Genestealers are not great against Daemons as the Daemons have invulnerable saves. It is all dependant on a number of factors really.
Rork: In the dark future of the 41st millennium there is only friendship.
Fenrir: and magic.
Kaiser-: My Little Chaos Marine, Friendship is Heresy?
Also for stealers, you pretty much want to ALWAYS get the charge, especially when the other major benifits to your unit are null (rending)
"The Lady Demands"
Watch the sniperfexes and dakkafexes tear them a new one. Their only issue is the lack of reliable armor piercing, which makes no difference at all to the Daemons.
Barbed Stranglers= ridiculously nasty. Plus just throw a Hive Tyrant at the Soul Grinder and watch it go down without touching your HT. Almost every time.
Plus, even our little gribblies can knock Daemons out in no time. High Volume of firepower= lots of death, since Daemons trade good saves for invuln. saves.
CC wise, I wouldn't even bother. I rarely play a CC oriented Tyranid army anyway, but the only thing I would try to hit with my 'Stealers are Daemon Princes, since they're normally alone.
With the Bloodchrushers of Khorne I don't think anything can touch Daemons in close quarter combat. Even our dakka Nids can't effectively put down more than one model per turn. And once Close combat starts I think we are finished. Our Fexes wont get to attack, and our Tyrants will fall very quickly to the mass S 5 or 6 attacks depending on the charge. Also we don't have anything to really deal with the plaguebearers which tie up our stealers, while they wait for anything else to come by and finish us off.
I haven't looked at Bloodcrushers vs. Tyrant Guard which could be close, except they have power weapons and we have rending and they have an invulnerable save when we do rend.
Plus I don't think most people really think that we excell at close quarter combat anymore. There are so many things that are more effective and point effecient.
In short: Nids can indeed beat chaos deamons in CC.
I found this calculator, you can test CC units against each other. It has some useful setting too, like random charge direction etc.
For example, I tried a 10 bloodletters vs 10 genestealers. Genestealer won 496/500 combat resolutions. You can also check the combat log for yourself etc.
Also, it seems that about 20 gaunts and 10 bloodletters are about 50/50 at winning combat resolutions.
EDIT: Oh, it seems to be this is a calculator for 4th edition...
Tyranids Win / Draw /Lost 
Daemon Hunters Win / Draw / Lost 
With deamons it realy depends on what you fight. Obviously thers not a lot we can use to beat khorne but vs slanesh we have some options, genestealers or tyrants would work nicly i recon. Nurgle will just waist our time, but they wont kill too many of us in return and tzench (im not even going to try and spell that one) is ranged. however what can help is movement. whilst not in out and out combat, if you can manage to cover a lot of the board before the demons turn up, theyll have to land near the back of the board. Then shoot them, and follow up in assault. Oh and by the way raveners actually do a nice amount of damage vs deamons. im not sure of the stats but 36 WS and I5 attacks, will kill off a fair few deamons. give them devourers or deathspitters and theres even more punishment. But in a straight fight, gaunts will not beat deamons.
Yes, for some reason, people don't like whips. They make many models pretty useless, and aren't that expensive. A Tyrant with 3 guards will deal 9 attacks in CC, and make models fighting them lose up to 3 attacks. Giving a few lashwhips to Warriors helps you if you want them to be heavy-CC, and not all of them need to carry them for it to be effective. Carnifexes, on the other hand, probably shouldn't use them.