Japanese. I know only a very a small amount, but I like the it sounds and I love the culture. The French language I sometimes like, esp. in music, but I personally think the pronunciations are very difficult and sometime the sound irritates me. In school, my second language, however, is Latin, which is much closer to French.
hm... im not sure which ones more useful but in all honesty id go with Japanese. but its up to you, i mean i don't know if you will ever meet anyone french in your life, which you might since you study languages, so... i dunno, im neutral on this now.