Haren is one of the most rock solid SP options in fantasy. He always seems to go undervalued. He can pitch and is a great ace to anchor a staff.
Lester hasn't lived up to his potential IMO. He has the capability to outproduce Haren across the board, but this "breakout" may never come. For now, he is the lesser pitcher, but I think it is closer than some people have suggested.
so i guess my question is for the next 4 seasons (this year and the 3 i can keep him for) which pitcher would you rather have?
Because of this, I would go with Lester. Age is in Lester's favor and if he does have a breakthrough season, you'll be golden with him on your team during his prime years.