Which is easier... depends. Assuming you are talking about two kilts of eaqual yardages, then it would be knife pleating. The reason is because to make a box pleat, you first have to make a knife pleat -- the "boxing" of it is another step.

However, when you factor in that most box pleated kilts are four yard, and most knife pleated kilts are eight yard, then I'd have to say a box pleated kilt is easier to make, because you are talking about far less pleats in toto.

Aye,
Matt

(take your time, Hamish)!