It appears from this study that both parties are correct to a degree. The first part covers the lower pec activation and the second part covers upper pec activation. This also covers grip width. See foot for references.
Barnett et al (1995)
The Sternocostal Head
One of the most common assumptions in the world of iron is that the decline bench is the best for developing the lower pecs. However, this familiar premise may be nothing more than another unfounded gym myth. According to the Barnett EMG study, the flat bench produced much more electrical energy in the lower pecs than did either the decline or incline positions. "I agree with this research" says NPC National Champion and pro bodybuilder Jay Cutler, "The flat bench is much better for lower pec development than the decline."
But what is the best grip to use? EMG studies have also shown that when doing the flat bench, the muscle fibers of the lower pecs are activated the most when using a wide grip. "This is very much true," adds Fred "Dr. Squat" Hatfield, Ph.D. "A wide grip with the elbows out will cause much more lower pec activation." However, whether you choose to use a wide or narrow grip, we can assume that using the decline position to target the lower pecs is just not justified. Eddie Robinson, IFBB pro bodybuilder states, "I feel the flat bench press, with a wide grip is best for over all pec development, but you do not want to go so wide with the grip that you over stress the shoulders."
The Clavicular Head
Now we all know that the incline bench hits the upper pecs. Right? Since the upper pecs seem to help to raise the arm, this would make sense. The incline position would put the arm in more of a flexed position than either the flat or decline positions. According to EMG studies this advice seems to be pretty much true.
The Barnett study tells us that the incline position produces just slightly more electrical energy in the upper pecs that either the flat or decline positions. However, the flat bench was found to be very close. While the difference between the two was considered insignificant, the slight advantage of the incline over the flat bench in upper pec activation may be just what some of us need to further develop the upper pecs. "This is all very true," says Robinson.
"There is no doubt the incline bench hits the pecs more than the flat bench."
Cutler agrees and says, "I personally feel upper pec development is very important for a bodybuilder. So I concentrate more on the incline bench that I do the flat bench." While the incline position may provide slightly greater upper pec stimulation Hatfield contends,
"The same thing can be accomplished by using the flat bench. I would suggest lowering the bar to the upper pecs instead of the lower pecs (as normal), using a wide grip with the elbows out."
Nevertheless, if you are going to use the incline position to target the upper pecs, a narrower grip has been shown to best activate them. Professional bodybuilder Mike Francois agrees and says "A grip that is just a little bit wider than shoulder’s width really hits my upper pecs best." But Sal Arria, D.C., founder of the International Sport Science Association and former powerlifting champion warns: "Using a wide grip can involve too much front deltoid and can cause the deltoids to slam against the acronium process, causing trauma to the muscle."
So.....focusing on the highlighted parts, it seems the missing factor here is where you lower the bar to.
Now let's all make nice nice and go to another thread.
-2z-
References:
Barnett, C., Kippers, V., and Turner, P. (1995). Effects of variations of the bench press exercise on the EMG activity of five shoulder muscles. Journal of Strength and Conditioning Research. 9(4): 222-227.
Elliot, B.C., Wilson, G.J., and Kerr, G.K. (1989). A biomechanical analysis of the sticking region in the bench press. Medicine, Science, Sports and Exercise. 21(4): 450-462.
Lockhardt, R.D. (1974). Living Anatomy: A Photographic Atlas of Muscles in Action and Surface Contours, 7th ed. London: Farber & Farber.
McCaw, S.T. and Friday, J.J. (1994). A comparison of muscle activity between a free weight and machine bench press. Journal of Strength and Conditioning Research. 8(4):259-264.
Thompson, C.E. and Floyd, R.T. (1994). The shoulder joint. In: Manual of Structural Kinesiology, 12th ed. Smith, J.M. Ed. St. Louis, MS: Mosby-Year Book.