I currently use a Wizard for grinding inferno at mp5 to comfortably grind exp and items. This is relatively fast but sometimes (i'm guessing due to gear) I can run into problems that will hinder the speed of my grinding.
Monks and Barbarians seem to have an easier time, or at least don't die as often.
I am wondering if there is a concrete answer as to which is the very best and easiest class to grind with within relative level ranges? Or is it all down to gearing and the way you use your class?
Best Answer
On low MPs, archon wizard is the fastest for xp farming. They can (as of 1.08) keep up permanent archon and roll through hordes of monsters. They are also relatively cheap to set up as you can get a 150k dps archon wizard for 10-15m that can roll through mp2 in no time. For higher MPs, you'll have to swap to a CM build, but those are way more expensive to gear up than building a decent archon wizard.
On higher MPs, the best/fastest xp farming is barbarians using the tornado/ww setup. Barbs have the best survivability on higher MP due to the fact that they are the only class that can get life steal on the belt and also they have a passive that grants 3% life steal. Also, their perma WoTB means they are completely immune to crowd control, which is absolutely necessary on higher MPs. WoTB is actually pretty bad on low MPs because you kill monsters so fast its hard to generate the amount of fury required to keep it permanently up. However, their gear is super expensive and it will cost 200+m to set up a barb that can handle mp7+ with ease.
Monks can build a tempest rush + wave of light build that can farm quite fast, this build requires 4 piece innas (to make sweeping wind cost next to nothing) as well as additional spirit regen gear to maximize wave of light spam. Its quite possible to get enough spirit regen for perm tempest rush, the trick is to use a slow attack weapon (skorn is perfect for this build). WoL becomes less useful at higher MPs due to increasingly higher monster health, but well geared monks can still farm quite fast (as is the case with every class).
This all comes down to how much gold you have. If you can afford it, barbs farm the fastest, but their gear is the most expensive. Monks are relatively cheap to gear due to one with everything, and decent int wizard gear is the cheapest to find.
Note, both the archon and WoTB builds are likely to change in the future as Blizzard has repeatedly said that they want to address the issue of perma archon and perma wotb.