Tangs plays much more on the PK than either Landy or MacK, indicating that he is better in his own zone. Or at least Roy is more comfortable with him back there. Iginla plays as much D as either, so a wash.
The RoR Tangs Iggy line is what I consider an almost ideal 2nd line. It is the line you can match up with the other teams top line. Can beat them by shutting them down, or by outscoring them.
Duchene, Landy and MacK is solid as well, not quite as good defensively, but on paper, better point producing. But it leaves 3rd/4th lines full of holes and weaknesses. McGinn and Winchester being healthy would help...scratch Cliche and any one of the remaining wingers (bench Rendo and Briere if you want both lines to be 100% D focused). I would also like to see Everberg back up. Third line of McGinn, Mitchell and Briere would have some scoring punch (for a 3rd line); and 4th line of E-flow, Rendo, and Winchester would be high energy and maybe even score some..without either being totally suspect defensively. Not sure on PK pairs with that lineup, though it could be worked out. And it would never happen unless the players I would scratch are injured...and even then, Roy would probably call up Carey or some such. Also not sure who would take on the duty of getting beat up for the sake of momentum.