If you want massive delts, here is the simplified version:
1.) Learn how to properly do side and rear lateral raises.
2.) Get super strong on side and rear lateral raises.
3.) Get super strong on overhead presses.
Although accomplishing these things may be easier said than done, by the time you do achieve them, you will have monster delts...period. This formula never fails, just like 1 + 1 always equals 2.
You might be thinking "shouldn't we be using the same formula (progressive resistance and proper technique) for every bodypart"? To that I would say yes. However, you might be surprised at how many people fail to employ these principles when it comes to their side and rear delts. Now, you will frequently see people doing heavy overhead presses...and while overhead movements are important for maximizing front delt mass, the front delts make up a relatively small portion of one's (potential) overall shoulder size.
This is why knowing how to properly perform side and rear laterals, while simultaneously focusing on progressive resistance, is so vitally important. Working primarily on overhead presses in order to get big delts is the equivalent of trying to get big triceps by focusing mainly on triceps kickbacks. It just doesn't work. In the same way, way to many people overly emphasize overhead pressing at the expense of side and rear lateral work...and they never achieve the round, bowling ball look they desire. Much of the reason for this is because they've been told that compound movements are what build the most mass...and that they need to put the most effort into them if they want to get as big as possible.
While this may stand true for most bodyparts (focusing in compound movements), it does NOT stand true for the delts, which is really 3 separate muscles in one, all of which have different functions and which require different movements in order to work properly. require completely different exercises in order to properly stress the individual muscles. You can't rely on compound movements (overhead presses) alone and expect to grow giant delts. This may work for bodyparts like the legs, chest, or back, in which compound movements alone are capable of producing massive development. This is not so for the delts. You can overhead press your ass off until the cows come home and still have relatively small, shitty delts.
Remember, when it comes to the side and rear delts, there aren't really any "compound" exercises for them. Sure, you could say that rows are a compound exercise for the rear delts and wide grip upright rows are a compound exercises for the side delts. But...unlike other bodyparts, in which compound exercises are going to add the most mass, this does NOT stand true for the side and rear delts. For the side and rear delts, isolation exercises (i.e. lateral raises) are king.
In addition to most people not knowing how to properly perform lateral raises, rarely do they use truly impressive weights. This is why their delts suck. If you want huge delts, you need to get beastly strong on laterals. This means that you need to treat them just like you would squats, rows, bench presses, or any other compound movement...because from an effectiveness standpoint, laterals ARE compound movements for the side and rear delts.
Exercise selection is another issue. Unlike many other bodyparts, in which free weights are usually equally or even more effective than their machine counterpart, machine will OFTEN provide superior results for the side and rear delts.
The reverse peck deck is one of the very best rear delt builders in a bodybuilder's repertoire. For many people they are vastly superior to dumbbell rear laterals, as they have a superior strength curve and make isolation of the rear delts much easier. This can allow the bodybuilder to really pile on the weight, dig in, and blast the hell out of his rear delts.
The same can even be said of machine side laterals. While dumbbell side laterals can be extremely effective, a properly designed side lateral machine has many of the same benefits that the reverse peck deck does, while also providing the additional benefit of reduced joint (i.e. elbow) stress. Like the reverse peck deck, a properly designed side lateral machine has a more even strength curve (compared to dumbbells) and automatically places the body in the proper alignment, thereby making isolation of the target muscle easier to achieve.
At the same time, a poorly designed side delt machine is an absolutely horrible choice. In this case dumbbell laterals are far superior. Before I go further, allow me to say that I don't believe that machine side laterals are necessarily better than dumbbell side laterals. When it comes to the rear delts I do believe the reverse peck deck is superior, in general. However, by applying proper technique, the initial shortcomings of dumbbells side laterals (uneven strength curve, etc.) can be overcome, making them highly effective.
Anyway, that's all for me right now. I NEED TO EAT!