There is no definite answer to this question. It depends on how you were taught. I keep taking classes because I really enjoy the socializing that goes with the teaching and learning. I've never taken a class from a teacher who hasn't said that you need to do the sides first and the top and bottom last. Everyone seems to think that the shorter lengths are easier to measure and handle. It also seems to lessen the chance of distorting the finished quilt top.
And thanks, Jan, for taking the spelling issue to heart. I tell people that I am probably one of two people in the world today who won't split an infinitive! I love to read paragraphs with good grammar and proper spelling.