Keep in mind...
An essence goes for ~ 700 gold on AH at the moment
You can vendor rares for ~2000-3000 gold at the most
If you do want to unload at the end of your run do not pick up these items because they will never ever roll good and they aren't worth the space in your inventory.
Never pick these up
2h Weapons - Yes all 2h's. The reason? Skorn and Manticore. The chance of you rolling similar stats to a Skorn with the same dps is outrageously low, low enough that you can bet on it never ever happening. You will never roll a 2h Xbow better than a decently priced Manticore.
Chance of being good - .01/10
Wands - There is a reasonable chance that you could get a decent wand. Well, reasonable compared to the chance of getting a worthy of carrying 2h item. Put it this way. If a wand has 880 dps, +10 max crit, 800 loh, 60%cd, 2.8% life steal AND a socket, it still will only fetch you one million gold. If it has +APOC it would sell, but that would leave it with too many affixes to be possible. So, don't bother picking it up. Why? They won't sell because Chantodos will always be better.
**** Thanks to Xane for pointing this out **** - DESOLATOR Wands are worth picking up
(ilvl 63) because there are Wizard builds that do not use Chantodo's
Chance of being good - .5/10
Helms - Even if you pick up a miracle helm that has 6% cc, socket Vit main stat over 100 and 80 AR, Mempo's is still better. Ik's helm is still better (and cheap) Nats can be better (set bonuses are important), hell for monks visage of guya is better. Not to mention tals helm which is also better etc. These are all cheap legendaries to buy. Don't pick up helms. Why? Anything else is better than a rare helm.
Chance of being good - .01/10
Boots - Ice climbers will always be better. Boots can not roll life %. Fire walkers have a good chance of being better. Nats and IK boots are better. Zunis are better, you get the point. Worthless rares, will never be worth anything. Leave them on the ground for the fallen grunts to play with.
Chance of being good - .03/10
Shields - No one anywhere EVER in d3 who knows what they are doing uses a shield. Unless they are trying out a funky echoing fury + shield chakram build at least. These will never be good, and if it is good, it will never sell, because shields are absolutely useless.
Chance of being good - 0
Rarely Pick These Up
1h Xbows - Calamity. Sometimes another 1h rare xbow can be good, but it is a rare occurrence, and most people use Manticore anyways.
Chance of being good - 3/10
Sources and Fetishes - Need a complete perfect roll, and there are many affordable alternatives even if you roll perfectly on either one. Avoid
Chance of being good - 2/10
Belts/Mighty Belts - Mighty Belts will never be better than the Legendary/set alternatives which are DIRT cheap. Belts are sort of worth picking up because they can be a stepping stone to a Witching Hour for Wizards and Witch Doctors. Monks + DH's will use Inna's belt instead, and Barbs will use Mighty belts. Anyways, there's a very low chance they will be useful, but pick them up if you want as they only take up one slot.
Chance of being good - (M.Belt .001/10 ~ Belt 1/10)
Pick These Up
Rings + Ammys The only piece that has higher or equal potential than any other quality. Obviously always pick up, Hell only unload once your inventory is full of these if you're smart.
Chance of being good - (10/10) ((Best chance to roll well)
Shoulders Shoulders can roll just as good as vile wards, pick em up!
Chance of being good - (8/10)
1h Weapons - 1h Weapons can roll good enough that people will use them. Some are generally more sought than others, in this order. (Higher % to sell) Axe, Sword, Dagger, Hammer, Spear(Lower % to sell).
Chance of being good - (8/10)~Axe (7/10)~Sword (5/10)~Dagger (5/10)~Hammer (4/10)~Spear
Bracers - Will generally be replaced by lacunis end game, but it is still very hard to get a good pair of lacunis that you won't have to switch out for survivability. Worth picking up
Chance of being good - (6/10)
Gloves - Have the highest potential of being BIS even than legendaries. Your best shot at finding something good, but it'll have to roll really well.
Chance of being good - (9/10)
Pants and Chest Armor These rare drops have the potential to roll good enough that they will sell, pick these up.
Chance of being good - (5/10)
So that's it! A quick guide to what rares to pick up, what rares NOT to pick up, and why.
Questions Comments Welcome! I hope this makes your runs more efficient and you waste less time vendoring something for 2k instead of running into piles of 3000 gold every second on the ground.