The best plug-in set you can buy is the one that saves you the most time with the type of effects that you do the most often. For me, it's the Magic Bullet and Trapcode suites. For someone else it may be Boris FX, for someone else they may want Zaxwerks or Element 3D and a bunch of the Video Co-pilot stuff. Since we don't have any idea what your style is or what kind of projects you are going to be working on pointing you to the "best" is very hard to do.
the kind of works I do in after effects are just 2d motion graphics of course I want to add good particles just like what I am doing in nuke (but not 3d), also footage I think I need green screen just like primatte or better, I also need a plugin that will shapen the footages form our poor-man's-dslr t1i and sony a57 . maybe I will just import 3d cameras from maya.