I am a CS student with a strong background in engineering and numerical mathematics. But now I want to play around a little bit with symbolic maths packages a little bit. Which one should I learn? Cost is a factor. I can work on either Linux or Windows. Might be playing a little bit with calculus and number theory to start.
I've heard very good things from people whose opinions I trust about Sage via Python. I would be interested in seeing a variety of opinions from others.