As you grow, you may find this particular advice unimportant. The smaller the variable type, the faster the program run. The former need 32 adding process while the latter only need 16 adding process. Of course, you have to watch out for the limit. In a competition, watch out for execution-time limit.
Efficiency is important.
But also take this into mind, don't be too efficient if it makes the program a lot complicated. Always try to be simple. If you find that your program too slow, first of all try to think for another way. If you can't find any, you then develop short cuts. Get used to the platform.