2-ply or 3-ply?

Back to the house-clearing and these knitting patterns seemed to tickle my sister's fancy when she came across them! She claims she was never on the receiving end of a vest & knickers combo gift set but I'm not too sure, one of these patterns looked well used. Anyway, I wonder which was best, 2-ply or 3-ply?

Off to the tenpin soon and it's crunch time. If we don't win we're definitely relegated. No pressure then!