This is a toughie, and my first instinct is to say take the course that interests you more or perhaps has the better instructor because, after all, education is about learning and improving your mind. But unfortunately because of the highly competitive nature of the college application process, other practical considerations must be weighed. A few that come to mind, are the classes weighted differently for GPA/ranking purposes, will one class take less time and effort to make a top grade (@menloparkmom makes a great point in post #6), is 1 teacher a potentially strong LoR writer for you? Also you need to take a look at foreign language “suggestions” for the schools you are interested in as pointed out by @happy1 in post #1. Will you be automatically rejected if you only got to Latin III, no, but that’s a potential negative that may get thrown in the mix, but still it’s your overall body of work that is considered in the context of what your school offers.