I read somewhere recently, that blender is the fastest developing 3d application in the world, and I’d believe that. I’d say that if your starting at 3d work, then start with blender, as there is a great comunity of help and tutorials out there, blender will only get better than other programs at the rate its developing and what you learn in blender wont take too much to convert over to maya or 3ds.
I started in cinema 4d, then went to 3ds and now am mucking around in blender, and I would have to say that they all have adventages and disadvantages. However, if I were to choose 2 programs to learn off by heart, I’d say it would be blender and maya (though I haven’t done any maya yet, I hope to soon). The reason for this is that blender is awesome for modelling texturing etc, where as maya (from what Ive been told) may be best for rigging characters, animation and rendering etc.
Your situation will also inpact on your decision. Are you looking into starting your own company? If so, learn what you want. Are you looking in starting work with another company, if so ask them what they want you to learn. I think you will find that not many major production companies out there use blender YET. Again though, being a free tool, if you get good at blender as well as one other program they use (eg. maya) maybe they wouldn’t mind you using blender as long as it ends up in a maya format.
Putting all this into one sentence: I advise you learn blender first, then decide what program you need to specialise in.