Deca is awesome for a few reasons.
The first is the fact that it is an excellent mass building compound. Not just for the anabolic effect but for the effect it has on your nervous system. Ok everyone get ready for one of my rants on the fine nuances of lifting weights. :-0
Deca helps to keep joints from hurting in a major way. Because of this you can lift much much heavier weight. This forces more blood in the muscles which will FORCE THEM TO GROW. Deca helps you to not have to be a volume trainer but a heavy ass weight trainer. (See Ronnie and Branch)
Whats more is it lets you put much much more stress on your central nervous system when you lift heavier. This is something that many people overlook. The heavier you lift the more pressure you put on your brain! Your brain will help you to compensate for this pressure being put on it and will literally help your body to adjust and evolve to cope with this extra stress. Deca not only makes you stronger, harder, painless, and hungrier but it also lets you account for the body based on the way it helps you train.
Think about when you take some heavy ass weight off and your eyes literally shake inside your head. THen when you put the weight back down you feel light headed, almost sick, and your legs feel heavy after a bench press. That is your body telling you to knock it off. You tell it to fuck off because you aren't hurt. You tell it I am going to keep doing this so you better get on board.
I promise if you aren't doing this to your body you are missing out on some great pumps and gains. I have had several nose bleeds after a squat or bench session with a heavy single or double.
The other reason deca is awesome is because it is easy as hell to get and get good stuff. It is not often faked like NPP because there are so many places to get raws. I feel confident in at least 3 of my sources that it is always deca. You can tell right away because if you get sore after 3-4 weeks your shit is bunk. You also don't need to do massive amounts of it. The sides are low if you make sure you keep the test ratio in line.
Anyone that doesn't like deca aint lifting heavy enough! Just my .02 cents