No idea how the pools are set up. I just occasionally check whether there's a contest that I might actually get somewhere near the top, depending on the contest itself (I don't bother with the tower ones, since I don't care for PvP) and whether I'll be able to play much. Oh, and saving up a small stack of books helps as well. There's really little hurry for me to level all my girls, my stats are off scale by now anyway.