Ok. Every enemy in the game has the same base chance to drop Engrams. You have the exact same chance to get a Legendary Engram from a level 2 Dreg as you do from a level 30 Captain. The best place to farm engrams is to do the Roc playlist. That is actually the best place to farm rewards period. For the time being get all of the Vanguard and Crucible marks that you can. Use those marks to buy your first set of Legendary gear, which when upgraded will take you to level 31. Also shoot for an Exotic helm... try to grab one from Xur. This way you need a total of 225 Marks and 1 commendation (75 for Boots, 75 for Gloves, 75 + 1 commendation for Chest) and with the Exotic helm you are at 31. Then farm Nightfall every week, do the Weekly for coins to buy stuff from Xur, and do the Daily Mission for Assendants to upgrade later gear. When you hit 30 also try to solo Crotas End, at least the first 2 parts and get the 1st chest. There is a metric a$$ton of youtube videos to show you how. That is honestly, a lot faster then just killing stuff over and over while praying for RNGeebus to bless you with a 0.00014% chance for a Legendary Engram (number pulled out of my butt)