Unfortunately I think the entire attribute system in TR is kind of broken at the moment. None of them have a big impact on how your character plays. I am hoping they realize and address this issue.
So, I've been playing both a soldier and a specialist/biotechnician in the game. I find that my biotech has a much harder time downing enemies. At level 15 or 16 now, and I still can't take out Rotting Sal or any of the Stalkers. My soldier is level 8 so I haven't really had a chance to try those mobs with him.
So basically, I'm going to start with a soldier but branch via cloning for several different characters. My strategy is going to be max firearms, because firearms will always be useful, maybe 3 points in lightening. I'm not going to put any points in armor except for the final armor that the character will be going to. I honestly hate the idea of putting points into armor thats going to become obsolete later on. Unfortunately this is one of the flaws of TRs progression system.
Also, with my biotech, I defintely feel like Decay is a waste of points. I'm also not that pleased with my injection gun, though its nice it does surpass armor, i prefer to kill enemies from far away.