Pre-calculus is necessary if you are planning to take any additional mathematics that focus on the calculus stream, but college algebra is often the last stop in any mathematics courses.  If your goals include any mathematics post-secondary, the pre-calc course will likely be more useful to you.  

It is surprising the number of post-secondary institutions that require even a limited form of calculus for programs that you would not expect to have any math requirements at all, and so pre-calc if you have the mathematical endurance for it, will keep your options open in a better way than college algebra.

I agree with a few of the above posts.

I know it may be early, however, you may want to consider "what you want to be when you grow up."  Think about your future college major.  If you plan on attempting a major in which not much (or very little) math is required, you could go ahead with the college algebra.

On the flip side, if you plan on majoring in science or engineering, you may want to take the Pre-Calc.

It really depends on your projected curriculum path.  If you need to take calculus for your college or career goals, you might want to go ahead and knock it out.  If you need to take a specific number of maths but not necessarily a specific level, you might want to take things a little slower.  Consider that your other courses are likely to increase in difficulty as well.  Are you so-so in your current class because of a lack of effort or because the subject is genuinely difficult for you?  Think about how much time you are willing to put into the class and how confident you are in the subject matter.  There may be other factors effecting your decision as well.  I know I personally chose to take College Algebra because the Pre-Cal teacher didn't use a teaching style I learned well with.  Talk it over with you parents or your guidance counselor and see what your best option is.

It all depend on your goals and work ethic. What are you planning on studying in the future and how much math do you need to accomplish that goal? Also it comes down to how much work are you planning to put in. If you decided to take pre-cal, are you willing to scarify some personal time to review an Algebra concept you forgot? 

The math is somewhat different in pre-calculus. In addition to algebra, it includes a lot of trigonometry.  Believe it or not, I don’t think I really understood algebra until I took calculus.  So don’t discount pre-calc.  It really depends on your goals though.  Do not take a course that seems to easy.  Take a look at why you are only so-so successful now.  It might be the teaching method and not you.  Having a different teacher or method can help.  I suggest you take a look at the text and syllabus for each course if possible.

In my opinion it depends on how confident you feel in your algebra ability. Pre-Calculus is likely to be the more advanced version of College Algerbra, so if you feel confident then I would go with pre-calc. 

Remember that mathematics is always building on previous concepts, so the new material will make a lot more sense if you have a solid understanding of the old material.

Another thing to consider is whether or not you plan on eventually taking Calculus. If so, you might want to do Pre-Calc. That said, both would be useful, so it's really a matter of how confident you feel and how much you want to be challenged.

Hope this helps!