As most of us understand, benches (flat, incline. decline) don't seem to give the results with the effort put into them. The DB's over BB's would be a better option for most. The path of DB's is more in harmony with the arc/path of the actually press. The "S" path to a lesser degree,but still important. A too set/fixed movement, with a BB, often invites injury. Another problem is that of going too heavy, too often. In most gym's you may notice that the guy's with the best pecs are the BB'ers over the heavy duty benchers. Repping out fast 220 to 270's, rather than going with slower 400+ 3-4 forced reps does have it's advantages. Than again, most men can't make up their mind if they want to be a BB'er or PL'er.
The bench press to the upper chest or neck (elbows out wide & inline with the neck/upper chest) may be the better option for more direct pec influence when using a BB (flat, incline, decline). Of course a pair of DB's would work very well with this exercise. In either case, the stretch/ROM will be greater. If new to this movement, warmup with care, use a much lighter weight than in regular benching and , most important, have a awake spotter near by. If training alone, a good advantage is to have a PR, rack or some type of stops.
Gironda advised benching this way. Don't know if he was the first to adapt this style. Probably not, he did borrow, and adapt, a lot of his exercise methods from those before him and during his time. West coast guy's were really very inventive when it came to BB'ing. Still are today from what I witness.
Dips (weighted) are an excellent pec builder. Not only a better stretch, but changing hand positions can affect upper/lower development in different ways, almost insuring a complete pec involvement. A steep Declines press can mock dips, but not to the same results that full dips can.
DB fly's are a short range direct pec exercise. Once the DB's reach roughly above 50 degrees, the tension is reduced off the pec's themselves to a greater degree. Cables have the advantage, over DB flys, of keeping most of the tension during the entire movement. A better option might be a Pec Deck, where the elbows lead the movement and a greater resistance/weight can be used., in all positions.
Might suggest: A pre-exhaust system. Some confuse this with a SS, which it is not.
1) Pec Deck 7-10 reps 3 sets
2) Dips 7-10 reps 3 sets
No rest between exercise 1 and 2, this is the first cycle. Rest 60 to 90 seconds between cycles. If no Peck Deck, than cables. If no cables than DB's.
If into conventional training, than do the dips first (3 sets) and than the extension movements (pec deck, cables, DB's), 3 sets. Good Luck.