The price of common/bronze cards was a lot higher in the first couple of weeks when more people were trying to get those 25 man collections, there are a lot less 100 stub cards now. A lot of bronzes are now only 50 or 60, while commons are sometimes more than that, some still over 100.
Generally it depends on who they play for, if it's a team who are easily collected then they are generally more valuable while catchers are also more valuable (not entirely sure why, presumably people feeding them to there created player?). Also, the lower the players rating the more valuable they tend to be, presumably because most people start at the bottom and work their way up when collecting?