All you hear about is how awesomely powerful Manticore is. You've seen people using Calamity and Dead Mans Legacy with great success and high DPS numbers. Heck, you've even seen people sporting a big old Windforce with an element of success (utilising its knockback skill).
So why dual wield...?
Dropping DML for another hand xbow seems pointless.
You get less attack speed.
You get less dexterity.
You get less crit chance.
You get less vitality.
Heck, in most cases you get less Sheet DPS.
You can get 10 discipline on DML too.
So why do it?
For me there's 2 main reasons:
Firstly and MOST importantly it looks AWESOME!
Secondly you can reach very high crit damage numbers. This is the closest you'll get to hitting hard like a big Xbow user, but also shooting at speed.
Basically it's pretty great all round, but you'll have to invest some serious gold in it.
Where do I make up the loss of vit, crit chance and dex from DML?
Users of DML are always going to have better EHP then dual weilders. They can make more of a choice to drop the vit in these areas and just go all out dps stats and other ehp stats.
You want to be looking for these stats in all your armour pieces ideally:
I have made up the grounds by obtaining Vit on amulet, bracers, shoulders, pants and boots. Getting all resist in some of these areas and belt + helm is also key.
For general survival (all round mp) you really need the following:
For boosting DPS numbers you want to aim for:
Gear choices break down
Andy visage - This helm is great for boosting DPS cheaply. It can roll with Vit or all resist for more EHP, but you will take an EHP hit when it comes to fire damage. It has crit chance too so this is a good budget option and not worth ruling out.
Overall it's not a great choice compared to:
Mempo of Twilight - This helm has everything. High dex, all resist, attack speed, %life and a socket. If you can get this with crit chance you never need another helm. If you can't get this with cc then go for a defensive stat like more vitality or go for a more offensive stat like extra dexterity.
Natalya's Sight - As suggested by Hyperion is another decent option, especially if mixing with the rest of the set. At 4 pieces you get a 20 discipline bonus which is nothing to be laughed at. It rolls with up to 100 dex, high armour and a socket. Random properties can also get you cc and more dex, vital or all res too. Worth a look at as an option.
Crafted Shoulders of Dexterity - an easy and cheap way to get high dex shoulders. Aim to get vitality, %life and all resists here.
Vile wards - If you have the gold it's easier to buy these. They generally have more armour then crafted shoulders so this is a boost. You can get very high dex and good amounts of vitality here and it's a great place to get that one stat everyone needs once, pickup radius.
Crafted Gloves - You can purchase some very nice rare ones, but any bet you'll be able to craft better ones for a fraction of the cost in most cases. Look for high dex, crit chance 9+, crit damage, attack speed and any defensive stats will be a bonus.
Sage's Gauntlets - can sometimes roll with some good stats for a demon hunter. I've come across these whilst searching for rare gloves with similar stats.
Rare and Crafted Amulets - are the best options IMO. You'll want to ideally look for average damage, high dex, crit chance 9+, crit damage and vitality. If you can't afford or craft these lucky stats then drop the average damage and make sure you get the vitality, amulet is a great place to stack this.
Natalya's Embrace - is pretty much unbeatable for me. You can get all the stats you need here. Dex, vitality or all resist, discipline, %life, 3 sockets, extra skill bonus and set bonus from additional pieces.
If you need to boost vitality you can get one with 160+ vitality and 90 dex. If you have enough vitality you can get one with 160+ dex and 90 vitality. It's a great item!
The inquisitor - can be a nice cloak. With additional move speed you may find you need this if you pick some other choices in armour slots. You won't be able to reach highest possible dps numbers using this cloak however. It does come with a standard 71-80 all resist.
Inna's Vast Expanse - As suggested by Hyperion this can be a great option to gain an awful lot of dex, life% and vitality in one piece as well as 3 sockets and 1 random magic property you can get a decent DPS/EHP chest piece right here. It does lack the discipline and skill bonus however, but if you feel you could do without that then this is an option.
Natalya's Bloody Footprints - will give you 2 set bonus to Nats set (7cc) and have some great stats of their own. High dex, all resists, damage reduction to melee attacks, run/walk speed. You can also get these with vitality.
Ice Climbers - are a good alternative option. They have great dex and vitality stats as well as a socket and all resists. Be prepared to lose the walk/run speed though (and the 2 set bonus from Nats).
Zunimassa's Journey (legacy) - the best ones on diabloprogress have +5% poison damage, 12 move speed, 79all resist 194 dex and 6% attack speed. Obviously, these are the best and this is a legacy item meaning they will remain that way. Expensive and hard to get.
Zunimassa's Trail - can roll with high dex (up to 200), vitality, all resists, move speed and 8% elemental damage. Pretty good all round boots.
Natalya's reflection - I highly recommend getting this ring here. The 3 set bonus is a godly 130 dex AND you get a min of 80 dex on this ring, not to mention a standard 8-9 attack speed. You can get this ring with crit chance, crit damage and average damage. I recommend looking out for one with average damage and crit chance if possible.
Ring 2 (all of the below are good choices)
The Wailing Host - is a great option for your second ring. Why this and not
Litany of the Undaunted? Basically the wailing host can roll with average damage as well as attack speed (2 random magic properties instead of 1). This is great for a dual wielder. A standard of 150-169 dex and 4.5cc on this ring make it a great choice.
Rare Rings - can roll with more stats you may need. You can look for rings with some vitality, armour or all resist if you need the EHP boost. I recommend looking out for ones with high average damage (xx-xx), some dexterity, attack speed and crit chance as well as any defensive stats. If you can squeeze crit damage on to it as well then you're in good shape.
Stone of Jordan - gets a worthy mention here. It has added % elemental damage that works great with black weapons such as Calamity and Danetta's. Extra discipline for more defensive tactics and vault spamming. Bonus damage to elites, which I can tell you now you won't be able to beat with any other ring, the extra damage to elites is godly at 30%, however your sheet dps and damage to trash mobs drops. The bonus damage to skill is also a great boost.
Unity - As suggested by SancticuS This can be as good, if not better in some cases then The Wailing Host ring. It actually rolls with very similar stats but also has +225–328 LoH on it. The random magic property you want will be attack speed or crit damage.