Before I start, I'll say that this isn't a technical question, more of a call for direction.
I've been using After Effects for several years now, and the quality of work has been fantastic. I enjoy the program's capabilities and couldn't be happier with the amount I have learned over the course of my last few projects. This being said, I feel that it is time to make the jump into the three dimensionsal world (a big jump, I know), and I guess I'm sort of stuck at this fork in the road.
I know the direction in which I want to design, yet I am not sure which program will suit me best. I've done plenty of readings on maya, 3ds, 4d, etc, and most comment on what your company prefers, what learning curve you are ready to take on and so forth. These are all great suggestions, but I still sit here pondering which road to take.
If there is more advice, please give it. If I am being a procrastinating bum, please reinforce this notion. Either way any insight would be appreciated. I'll leave you all with this: I think exactly WHAT I want to design may be the best indication of which direction I should lead. I am most interested in potentially modeling products for companies, putting together short presentations demonstrating a client's capabilities (sort of a how-to video), and so forth... Thanks for reading!
All 3D apps are going to be a new experience for you. I use Blender a lot. It has excellent integration with AE now and it's open source so it's free. It will run on about any computer. I also use C4D and Maya, but not so often. I just have them to integrate with a few of my clien'ts workflow's. C4D has excellent integration with AE.
C4D is used by a great number of AE artists and, as commercial 3D apps go it's fairly affordable. Lots of folks use 3D Studio Max, Maya, and other apps. It just depends on what you are going to do and what kind of production pipeline you have to work with. I usually recommend that folks on a budget start out with Blender and see if they like or are comfortable with 3D.
Here's one thing to consider. All 3D work uses basically the same theory but the keyboard shortcuts, UI, and interface are different. Those things all change some with each version of a program. It's more important to learn the theory than the software.