<p>I would take the science course.</p>
<p>Sure, it would look better to take four foreign language courses, but taking something equally/more rigorous will presumably not affect you negatively. </p>
<p>If you apply to a more science-oriented school, then I wouldn’t worry… If it’s a LAC, then I would suggest the Spanish course in order to be more well-rounded. Regardless, it doesn’t seem like it would make or break your decision.</p>
<p>“Recommend” can sometimes be a code word for “Require” or “Preferred.” Although that is more often the case with Math and English than it is with foreign languages or social studies/history. MIT, for example, recommends 4 years of math. I personally don’t think the applicant whose high school math sequence consisted of Algebra I, Algebra II and Geometry stands the proverbial snowball’s chance of admission to MIT. Someone whose high school math sequence was Calc I, II and III might be another matter.</p>
<p>I think the decision as to whether to take the fourth year of foreign language or the extra science class is one that should be determined in large part by which schools the OP plans to apply to and what they expect from their successful applicants.</p>