If McGinest was still here he'd have a better season overall, I think, especially if you are thinking in terms of team success.
Honestly if you were to have asked me I would have guessed that Seau would come here and be very mediocre considering how his years at Miami went, especially the last few. I am completely blown away at how much of a spark he is on defense and how much of an impact he has made. Belichick gave him credit for the safety due to his excellent coverage on Royal up the middle which left Losman with no options.
Seau looks completely rejuvinated and I hope he sticks around next year as well. He provides a lot of that same fire that McGinest provided last year when things weren't always going good.