If you're just taking one of the two, I'd say go with micro.
Macro deals with things like inflation, unemployment, trade, monetary aggregates etc.
Micro deals with the economic decisions made by the various actors (ie: businnesses vs. households), factors that affect supply and demand, the effects of taxes, absolute vs. comparative advantage.
That's what comes up off the top of my head..
edit:
I think in most schools, when it comes to intro econ courses, neither is a prereq for the other. So you can take either one.
Also, see if your school lets you take some kind of Economics for Engineers. It's neither micro or macro, but it's very useful imo.
You learn things like how to assess the profitability(or feasibility) of a project. It is meant to teach engineering students that resources (such as money) are an important factor in decision-making.