If you're able to get into MATH 1A03, and it ends up being your cup of tea, definitely consider taking 1AA3 as well. I picked up 1AA3 last minute in my first year, and it was a blast.
MATH 1B03 (Linear Algebra) was also pretty neat, but in a very different sort of way. I originally took it because I thought I wanted to get a math minor, though I later changed my mind on that.
To be honest, the best way to pick electives is to try to have them balance your schedule out and reflect your varied interests. Consider courses like Econ, Philosophy (in spite of long papers), Anthropology, etc.
Your electives are your chance to have a bit of fun.