Ok here it goes:
All the weapons are excelent when used against the apropiate foe in the right environment.
The pistol is a generally underrated weapon, whereas in open spaces it is your most lethal sniper weapon - the one and only mean to get rid of Jackals is you can't run over them.
Suprisingly this little sidearm is your next best thing to take down a Hunter with, when you're low on rockets.
The assault rifle is overrated, on higher difficulty it's almost useless against Elites and Jackals, because it takes too long to get down their shield.
It's usefullness is somewhat aproved in close quarter battles, especially against the flood.
The plasma pistol is a deadly tool, but it runs out of juice fast so use it only occasionaly if you have shielded targets or Sentinels on your track.
Ditch it for a plasma rifle - it has a better meele reach too.
BTW the infecters are good for your weapons' butt. Don't waster ammo if you don't have to.
The rifle is the ultimate flood killer - provided they don't flank you.
