Also, science courses in the summer are very time-consuming. I took Chem I and its lab last summer and for the whole month I was in it, my life revolved around studying for that class. I definitely could not have taken it with another summer class, because one science course itself requires at least a few hours of studying everyday.
But if you are really good at time management, and fast-paced learning, the choice is all up to you!
Best of luck!
I felt like classes such as the sociology or any philosophy courses are do-able during the summer, however, with another course. One summer, I took Intro to Sociology and Lifespan together and felt like both were manageable to study for in one summer session.