Which Math course is harder, linear algebra or differential equations?

Linear is definitely harder than differential.  That said, it also really depends on the professor, so look up who is teaching what class before you sign up.

take differential equations first. People have told me if you do that then linear algebra is really easy.

Differential equations is much harder. Differential equations is based on doing Calculus for actual figures, weather you're talking about a curve on a graph or a curve on a sphere expanding at a certain rate. All linear algebra is is a hard version of algebra that makes it easier to understand why lines work on a graph by in a much more complex way than simple algebra. Differential equations you have to work with equations too for something HAVING to equal something else, and in linear algebra you work with some equations, but not many. It's mostly working with formulas to discover how lines work and why they work. Differential equations is for any shape you can imagine. And differential equations can be where you're plotting 5 equations on a sphere at once and differentiating between them. Now that's hard. So if you want my advice, definitely take differential equations. It will benefit you more mathematically speaking than linear algebra. Good luck with your studies!