I guess it depends. If by "newcomer" you mean a rookie, I'd have to guess Larry Fitzgerald, Arizona Cardinals.
With Cardinals main receiver Boldin out for much of the year, if not all, Fitzgerald, who has great talent already will get even more catches.
Also, Shawn Andrews, OG for Eagles and Vince Wilfork, DT Pats will have big roles in winning teams at less glamorous positions.
Two other big time rookies will be Julius Jones, RB in Dallas and Kenechi Udeze, DE for Vikings.
Eli Manning may be a great QB down the road but like all rookies in modern day football, will struggle in his rookie season.
Oh yeah, and Sean Taylor with the Redskins has to be up there.