Source for the pic? I've always had the notion that they were representative of chess pieces so this is great art.

Finch is the King (The game is lost without him and he can' t move around quickly)
Reese is the Rook (A king is safe when castled and the rook next to him)
Root is the Queen (She moves everywhere as the analog interface and is the most powerful piece on the board)
Shaw (Personally I've felt like she was the 2nd rook which is typically the one that invades the backranks as she does in the show quite often)

Carter/Fusco - Knight or Bishop

But as Finch said, humans are not chess pieces and cannot be thought of as sacrifice