Really it won't matter in a long fight what you start with, as long as all of your dots are kept in rotation after the first initial round, we are only talking maybe 20-30 points of damage (at my level anyways) based on initial casting. I think the most important thing is to keep an eye on your dot times and keep them up, more so than worrying about the rotation. All the dots are on the same GCD just like other classes. I know that by starting with bio > miasma > bio II > thunder > Ruin, bio just wears off and I am able to instant cast it again. (rotation at lv. 30).
