Depends what kind of game you prefer, if you like struggling to build a team, select a low league and look at the media predictions/finances and pick a team that is predicted to do badly in that league (if its a really poor league it's usually fairly easy to make this team compete near the top anyway)
alternatively if you like signing decent players and playing attractive football try doing the opposite and pick a team predicted to finish at the top of their league.
Teams that have just been surprisingly relegated such as Monaco and Sampdoria would be decent choices too, as well as big clubs languishing in lower leagues like 1860 Munich, Perugia and Deportivo