Went off this game a few weeks after release and just recently came back to it after seeing more of Matrix's inferno runs. Though I was looking at my HP and I'm not even near 1K and that's only for the ranger.
Any places that's easy to farm and for all classes?
Also I'm assuming splitscreen is the way to go for farming, yes?
Mission 84. Kill all but one of the UFOs and then just stand there and shoot the streams of ants that fall out. Collect the drops. Repeat for hours on end. It goes faster if you have two controllers and you have the same class for both players. It doubles the armor increase speed. It saved a ton of time.
While farming, I'd suggest having something to do other than watching the TV!! My computer is next to my television, so I was watching DVDs on the computer while half ass paying attention to the game, pretty much only to make the pick ups.
EDIT - for weapons, I farmed in 71 Inferno by killing everything with the Wing Diver and letting the other class pick up the weapon drops.
Your name is sung and tattooed now on my heart - here I will carry you forever CarryTori Amos
Pretty much any mission of the 20 included are farming fiestas (swarms and bosses galore). Currently I've been farming mission 16 on Inferno looking for the last 5 weapons for my Wing Diver. It's caves populated by spiders, both normal and silver (silvers drop 3 items each), then 2 groups of golden ants at the end. Takes maybe 10 minutes, enemies are spaced so that there isn't too much worry of death if you're careful, and nets upwards of 20 weapons or more. Armors are more than abundant.
Aside from those, I'd say mission 28 - Brute Force in the regular campaign would net you the most armor.