RE: bent over rows
JH is on the money. Underhand grip means that the forearm is fully supinated and this shifts all the focus off the lats and on to the bi's.
One purpose of building a big strong back is to aid in benching (antagonistic muscle groups) and this means that you should be working through the same range of motion and grip as a bench press. Therefore, a slightly wider, over hand grip is the best IMO.