I think sides first and then top and bottom is what I've seen mostly in patterns unless they are mitered. If the sides are done last it makes the quilt look skinny even though it isn't.

"B" here too; I read somewhere - on here I think - that the sides go on first; then the top and bottoms, but guess it could be a personal preference. Think the B layout looks better though. Guess if it's square - it wouldn't matter.