I would say there are two school of philosophy here.

1. Spend time with only one program when you are a beginner, because it takes a lot of concentration to learn a complex piece of software, especially if you are unfamiliar with the subject matter.

2. As you get comfortable with the ONE piece of software, look around at others and "dink" with them to see noticable differences and similarities.

If you have played with 3d software before, explore more than one....If you are new, stick with one...at least for a little while...

-just my 2 cents.
:p