I've found the Pak43 be useful against the pershing commander in particular since there's no off maps or call in arty get rid of it. But in general, as long as your opponent(s) is playing a commander(s) which don't have a 1-click-kill on it you're going to be able to make use out of it, some examples are Shock Rifle, Guard Motor and the Pershing.
But always place the pak43 behind a building or other shotblocker, have a medic bunker and some reinforcement (or medic base as OKW) near it, constantly repair it if it's taking mortar fire. So basically babysit the thing.
