couldn't tell you. usually try to decide on my own. i use the stats at fftoday.com/stats
they have it all broken down by how many points are given up fantasy wise to each position. it's a useful tool if you want to check out your matchups from week to week. it is of course worth looking at the previous games to get an understanding of the break down. fluke games or weird games will skew the rankings a bit. so keep that in mind early in the season when there is a small sample size. good luck.