Once you've reached 60 and have started gaining paragon XP, leveling becomes a completely different game.
I ran a few 1-hour long trials when the paragon system was first introduced to figure out the best way to get paragon XP. But first a few disclaimers - these trials are not intended to tell you how fast you will get experience, but rather to be compared to each other. I am a tanky monk. I am not super-geared. Chances are you will farm a lot faster than me.
Starting point -------- EXP gained -- Notes
Act 1 Quest 1 -------- 4.1 million - Took ~35 minutes to get 5 stacks of NV
Act 1 Quest 5 -------- 5.2 million - Second hour (started with 5 stacks)
Act 2 Quest 1 -------- 5.2 million - Got 5 quickly
Act 2 Quest 4 -------- 5.1 million - Second hour (started with 5 stacks)
Act 2 Quest 1 (co-op) - 4.9 million - Partner was moving pretty slow
Act 2 Zulton Run ------ 6.0 million - My farming run of zulton's dungeons, oasis, and belial
Act 3 Quest 3 --------- 6.2 million - Got 5 stacks quickly
What I gathered from this information was that even when I measured the second hour of exp gain, which had the 75% Nephalim Valor bonus from the start, nothing compared to the amount of experience I got from an hour of play starting fresh in Act 3. I am not geared enough to do Act 4 yet, but I'm not sure its even worth testing as discussed below.
To farm exp efficiently you want two things: The first is a lot of experience per kill.
Experience per kill is determined by both monster level and the relative difficulty of the monster. I don't know if we have exact details on the experience gained for every type of monster, but you can assume it scales as mentioned in the 1.0.4 patch notes:
Monsters across the game have had a pass to make their experience and loot rewards more proportional to the effort required to kill them
For example, Imps and Tormented Stingers grant less XP and drop less items, but Lacuni Warriors grant increased XP and drop more items.
We do know the level of the monsters in each act though. And combined with this answer we can determine the following:
- Act 1: Level 60 = 100% exp gain
- Act 2: Level 61 = 115% exp gain
- Act 3: Level 62 = 120% exp gain
- Act 4: Level 62 = 120% exp gain
Act 4 should give roughly the same amount of experience as Act 3. But it sure seems a lot harder to clear, at least for me. I'll be skipping that act for XP farming.
The second thing you want for maximal XP gain is a lot of kills per minute. I don't have any hard data for this, but choose places to farm where you find large packs of creatures in areas that are close together.
The Cursed Hold in Act 1 or the Breached Keep in Act 3 are good areas for this. A large outdoor area where you may run for 10-20 seconds between fights is much less optimal - with 1 exception. The Fields of Slaughter in Act 3 tend to have a HUGE amount of creatures.
Nephalim Valor. Each stack gives you a 15% increase in experience gained. Get those 5 stacks quickly.
Rubies in Helms. A ruby will give you a percentage-based increase to all experience from monster kills. A permanent ~2 stacks of NV? Don't leave home without it.
Wearing items with +XP per kill. Debatable. I wouldn't bother. +XP isn't currently a possible affix for items level 60 or higher. Kills at this level give experience in the thousands. I'd much rather have a piece of gear that let me kill something more quickly than one with subpar stats and +20-50 experience per kill.
Follower with +XP items. Definitely worthwhile. You will only get 20% of the experience bonus, but what else is your follower good for?
Legendaries. Leoric's Signet and the set bonus for Cain's Fate both give percentage-based experience bonuses. The set is probably not worth using because it requires you to sacrifice 3 slots for some pretty bad items. But the signet is definitely worthwhile - at the cost of only 1 minor gear slot you can get up to a 30% experience bonus! Every power-leveler should get their hands on one.
Massacre/Destruction/etc bonuses. Massacre bonuses and Mighty Blows don't hurt since there's no extra effort to get them. But don't go out of your way for Destruction bonuses. Based on my experience you'd need to break a TON of stuff to even get close to reaching the amount of experience you get from a single monster kill. Don't waste the time.
Quests. Quests do not grant experience at level 60, just gold. Don't worry about them too much.
Co-op. Experience is not divided or shared. Every member of the group who was present for the kill gets the full experience for the kill. If you can clear stuff faster with a partner or group, do it. If your partner isn't pulling his weight and you are doing extra work, you're better off alone.
(AKA common sense)
- Don't farm in an Act that you can't quite handle. Dying and running back to where you left off wastes a lot of time.
- Try an offensive build instead of a defensive one to clear things faster.
- Have good gear to kill things faster.
- Get movement speed. Less downtime between packs and quicker corpse runs are good things.
Pick the highest act that you can clear without dying excessively. Clear areas that have lots of monsters. Put a ruby in your helm. Get 5 stacks of Nephalim Valor as quickly as you can. Put XP gear on your follower. Buy Leoric's Signet.
And most importantly...
Just keep killing. Just keep killing. Just keep killing, killing, killing. What do we do? We kill, kill.
-Dory, Finding Nemo (2003)