For a beginner, I would use a GS, so that you can block his charge, when he comes flying out of the ground. (For TRI) Other than that, learning how to dodge and roll, is a much better alternative. Truly any weapon can be used, its just the weapon that you find you're best with against said monster.
i would suggest using a blango longsword for its ice element and only using the shock trap when its enraged or when red gauge is on.. and i would recommended cutting of its tail but the first thing you should (First Thing don't damage it yet) do is to shock trap it then plant lg barrel bomb+ on its stomach
I always preferred a great sword or lance so I could easily get horns and tail. The great sword is exceptional at knocking him over if you can get between his legs and learn when and where to roll to avoid attacks.
I've been playing since the first MH and never really cared much for traps, but if I were to use them, I would likely use the time to get the tail off. His tail is harder to get than his horns since he'll be willing to keep his head toward you most of the time.
You can disregard a good portion of the above posts as they are mostly talking about stuff that is not in the 3rd gen games. For Diablos Raw damage is significantly preferred to element damage as he isn't very elementally weak. His tail is no longer a pellet magnet so that is a bad idea. The best strategy is either full raw(GS and the likes) or to use poison(SnS and the likes).
Speaking as one whot hates to hunt diablos, I have used an assortment of weapons. While hunting other monsters, I prefer hammer or SnS. With this guy, hammer was hard to keep charging, SnS kept getting me kicked over by his feet, bowguns were to hard to dodge with, Longswords were just awkward, but lance killed Diablos in record time for me.
Chandler8 wrote: Speaking as one whot hates to hunt diablos, I have used an assortment of weapons. While hunting other monsters, I prefer hammer or SnS. With this guy, hammer was hard to keep charging, SnS kept getting me kicked over by his feet, bowguns were to hard to dodge with, Longswords were just awkward, but lance killed Diablos in record time for me.
@Link1275 Diablos is actually pretty weak against Ice damage since 3U. I killed her (Black) with no traps or bombs in about 10 minutes with the Blizzarioths+ (Dual Blades).
As for the initial question, a rule of thumb I prefer is; The faster the monster, the faster your weapon needs to be. I'm an avid Hunting Horn user and have solo'd with it since Unite, but the HH is not the right weapon for the job with these things. Cutting damage is the way to go, and on terms of being fast and dealing out elemental damage, Dual Blades wins. Attack the same leg and go for the tail on staggers, you'll break off everything easily.
While Diablos' resistances to Ice may have changed, where the element is effective on him however you won't be hitting as often with the weapons that are elementally based. Those places that he is weak to Ice being: Head(20), Back/Wing(25), Wing Webbing(20), Tail Tip(30).
Diablos is however EXTREMELY weak to poison(initial Tolerance of 200, increase by 50, and 125 HP per infliction). And as you can build up poison while the monster is still inflicted with Blademaster weapons in MH3U, poison becomes a very effective weapon.
And while fast weapons work well on Diablos, so does just about every non-impact weapon. The rule of thumb on Diablos is to use something that you can feel comfortable getting away from his charges with, or blocking them with(I can use HBG on Diablos and rarely get hit in MH3U).
I concur with those statements, I did mention however I staggered it frequently to attack its tail. I would definitly use a pair of poison DS if I had them, simply becuase Poison is amazing in 3U. Since my only other option on me was a non-powerphial Switch-axe I wasn't too confident in killing it particularly fast with it haha.