I usually pose first. I find it difficult to pose the figure if I can't see it all, and clothes get in the way. Yes, you can hide the clothes...but why bother, when you can just dress them later? The only reason I can think of for clothing first is to get in the habit, for the times when you will be using items that are not conforming or smart-propped. Dynamic clothes, faery wings, hair that was designed for a different character. It's much easier to bring them in when the character is in the default position than to try and match the item up when the figure is posed.