For the melee weapons; Power Fist should obviously be the most single target destructive. That thing is literally an anti-tank weapon. It ought to be far better against, say, a Carnifex, than a machete could ever hope to be. In terms of massive single target damage it should be king. Currently the Combat Knife is pretty much the best melee weapon simply by virtue of being very fast and actually having better damage than much slower weapons in addition to its exceptional attack speed. 

The knife can stay FAST, but something is wrong when its damage on a hit is remotely comparable to a much slower Power Fist (single target) or Thunder Hammer (area of effect). And then you have the 'fast' weapons; the combat knife (single target) and the Chainsword and Power Sword (cleave). Also it is peculiar that the defining characteristic of the Chainsword (the chainsaw rev) requires an advanced perk to get rather than being standard.

As for ranged weapons; most of them feel very weak. With a few standouts. Bolters especially should be pretty punchy guns and currently do not seem that way. Making them hit much harder and having a much slower and more deliberate reload is probably called for.