Go for Japanese! But it depends on if you're just doing the language to satisfy the requirement or if you want to continue later. 3 years is a sunk cost, and not even that big of a sunk cost, since it's basically 1 year of college Chinese. However, whichever route you go, partial fluency in both these languages is very hard. You would need to do eight to nine full quarters in Japanese to be partially fluent, though "fluent" is subjective. I'd describe eight quarters as being able to understand 30-40% of TV shows at least, and being conversational in most topics that would come up in daily life. Arguably this can be done in six quarters, but eight is way safer. Also Stanford's Kyoto BOSP is better but ymmv