I do everything in game. There have been editors in the past for previous Maddens that I have toyed with but have never felt comfortable using. Mostly due to the transfer process. The nice thing about in game edits is that I can see things as I change them.
My overall process includes lots of Excel spreadsheets. I get rosters and stats and work towards setting up some initial "overall" ratings based on stats. Generally, I have several hours worth of out of game work getting everything set up in Excel. Then when I get into the game I have those spreadsheets ready to go. It takes anywhere from 1-2.5 hours per team in game. I start by moving people around based on experience(as close as possible), skin color, and size(again as close as possible). I give them the correct numbers during this phase. Once I have that complete for a team, I go back and edit names, equipment and ratings for that team.
That is far more information than you asked for, but figured I would let you in on the "inside" secrets. LOL Though it is a lot of work, I really enjoy creating the rosters. My wife thinks I'm crazy! She is probably right! But enjoy trying to create accurate representations of past seasons. I will say, not to brag on myself, but I feel my rosters play far superior to the default Madden rosters. EA should fire Donny and hire me. LOL