No matter what type of belt and buckle combo you wear, you'll find that it's incorrect. Personally I strap anything long enough around my waist and stand by to be adjusted accordingly to whatever is the fancy of the moment. And then I still manage to get it wrong!
Last time I was on parade in No 2's, which was Nov 03, the correct belt was the new green cotton type one. It's like a 58 pattern belt, but without the holes. That said, there were 4 or 5 differing types of belt combination on display! Personally speaking I used to like the old plastic belt with big metal buckle. For those of us below the rank of WO1, the correct belt is sh1t and this really needs looked at.