It's best to take more credits and get high grades, but that isn't an option you listed. Why are you supposing that more credits will equate to you earning lower grades? 12 credits is probably full-time at your school, but you should pile another class on top of that to bring your total to at least 15-16 credits each semester. Having a heavier courseload will demonstrate your maturity and ability to handle such a load. Of course, don't pile on the courses until you drown yourself, but challenge yourself. Nearly anybody can do well in science courses if they only have one -- the true test comes when you are taking biochemistry, pathophysiology and other classes. This semester, I have:
Biochemistry 3
Honors Lit. 3
Bible as Lit. 3
Physics & Lab 4
Spanish 4
Pathophys. 3
TA Physiology 1
That totals 21 credit hours. I certainly don't recommend this (particularly if you aren't accustomed to the college experience), but I've found that this number of credits keeps me motivated, challenges me, and that I'm still able to get above a 3.5 every semester with this number of credits. I also work 15 hours a week, am married, and have a seven-month old son. It isn't impossible, and it keeps me focused most of the time.
When I was a sophomore/junior, I was equally busy. I carried 17-22 credits through each of those four semesters (lowest semester GPA was a 3.48), and worked 40 hours a week for those two years. Once again, not easy, but fairly doable. Anything less and I would be bored!
