Pistols/rifles are useful. Don't invest in swimming or environmental hazards (or whatever it's called).
Also, you might want to not invest too heavily in heavy weapons, since from what I remember, the heavy weapons either suck or can be used just fine at lower training levels.
Also, this is seriously like the third time you've asked what skills are important.
--
Ginhyun
http://img.imgcake.com/nio/7ginpngam.png