the easiest place would be the zone on venus with the crashed ship in the middle just after the library the enemies spawn so quickly that you can have a full fireteam of 3 or even 6-10 people in the area and u will not run out of enemies to kill and every hour a huge wave of majors spawn for both vex and fallen ;D there's my secret guys do with it what you will

Well - i only get good items from there when the message apears "our enemys fighting each other" Then a massive Fight is there with some Yellow Guys etc. They drop maaaaany blue items

Alot of people farm the area in Venus, too. From the start go past the first pack, go left. At the next pack go left, up the stairs, down the hole on the left, follow that around and up into a Vex versus Fallen battle, go right past all that and out the other end, follow that and then you are lead to another area with Vex versus Fallen. Farm that area repeatedly. Lots of Spirit Blooms spawn as well. It follows a spawn rotation, after you cleared it all 4 or 5 times the next wave is like ALL yellows. Once you cleared that it goes quiet for 1 minute and starts over.

Mars