I'm not gonna get into a training theory discussion with guys on the anabolic board because maybe 10 of them tops even know how to lift.
Flyes are a waste of time, as are x-overs and any variant of the two.....pullovers, 'lol' is about all I can say, expand that ribcage (even though it's physiologically impossible)......Dips are a great exercise, same deal for inclines and declines, dumbells have their place as well....the flat bench is a great lift too. Great because of the load you can apply to your upper body. Sure, it's over emphasized by douche bag gym rats and frat boy lifters......and as SS said, many an idiot has injured their shoulders by flaring their elbows trying to "isolate the chest", but when done correctly it can place a lot more stimulus for growth on the upper body than d-bells or inclines just because it's possible to handle more weight, thus greater stimulus.
I am expecting the requisite silly responses, like incline flyes, flat dumbells, and pec deck are BEST for mass, or benching hurt my shoulder, I use incline d-bells and smith machine bench......
Really, a barbell press (pick one of the 3) trained progressively is what it boils down to, dumbells can add volume and total workload and not drive you towards overtraining and hitting a wall because the load is less.
The flat bench is to overload, it is a COMPOUND lift, it trains the upper-body....shoulder girdle, triceps, and you get some crazy tit size from it.....people who think it doesn't isolate the chest are morons because that's not the point of the lift.....people who say you ''feel'' incline d-bells better don't understand the role load plays on stimulus for growth (they're either tiny, or they just take more gear so that their crappy training is adequate stimulus).......really, it's not worth debating on a ''bodybuilding'' board like this, unless it comes up in the training forum where there is a good group of core posters who know training.....not knocking the other forums, but you're more likely to get "what's the BEST exercise to build massive pecs like Brad Pitt in Fight Club" over there than over here if ya know what I'm saying.