Commandos are really effective. Can almost see in darkness, can kill hordes of ZEDs with timed headshots, ZED-time extensions...
I am a more dedicated player, and while Commandos are not ultimatively powerful, they are allrounders, suitable for most situations. I do not know how many times I saved some idiot running through the high gras in the middle of a wave with my scar and seeing abilities. Commandos do not need a flashlight. They see the health of an enemy, that is usually enough to decapitate them.
As far as scrakes go, unload a tip of your Scar into their head just to make it not charge towards you, reload, finish it off if there is noone around. This costs a lot of ammo especially on suicidal, so if you have the option, get a tad of distance, notify your team, take it down.
Fleshpounds are a difficult matter, though. In later waves I mostly find myself with enough money to have a pipebomb ready to soften it up, and it saved me quite a few times. This also works well in solo. If there are other players around, it may still be better to type in "FP" and get some distance.