Learn C and learn computer science. Let's get away from subjective "shoulds" and talk about practical stuff. You want to learn things, as much as possible, tha

Learn C and learn computer science. Let's get away from subjective "shoulds" and talk about practical stuff. You want to learn things, as much as possible, that (a) are likely to remain useful in 15 years and (b) are going to qualify you for the highest quality of jobs. C, as a language, passes this test. So do the fundamentals of computer science; they may not bring you quantity in job opportunities, but they'll give you access to quality. Aside from that? Well, it's hard to predict the future. I can't make individual calls. Who would have thought JavaScript would be so popular in 2014? The whole language is a hack. But if you learned it in 2000, you still have a high-demand skill set. Learning one thing or one small set of things won't do, though. You need to future-proof yourself with a wider knowledge portfolio, and very few jobs will teach a person to do that. On the other hand, if you learn a lot of useless and parochial crap that won't generalize (i.e. the quirks of your own corporate codebase) you get to a semi-depressed state of "learnout" (you struggle to assimilate new things, because you've filled your brain with unrewarding crap) and that's no good either.