Big Daddy
Lots of people are benching like bodybuilders with elbows flared and their shoulders taking the brunt. Would be time to watch Dave Tate's vid and learn how to bench correctly. How do you think people bench 500-800 pounds and have no shoulder problems but you are benching 100-300 pounds and you are experiencing issues.
Umm... possibly because they are bodybuilding?
I agree that powerlifting style benching is safer on the shoulders, but it definitely works the chest less. It allows you to shift bigger poundages but what does this matter to a guy training purely for size for whom the sole purpose of the bench press is to contract the relevant muscles and make them grow?
I started benching 'properly' recently and this conicided with a shift to more strength based training. I want a big bench, hypertrophy is still important but I let my assistance stuff like Dips and Incline handle that. As for the main lift, it's all about getting as many muscles into the equation and pressing the most weight.
But if you're benching just to get big pecs, tris and delts then I can't see much of a problem benching with a flat back and elbows flared, etc, as long as the trainer has his shoulder mobility and general shoulder health sorted out and keeps his form slow and controlled. Bodybuilders have been doing it for years without much problems!
But as stephen77 has said, the OP has not told us whether he is training primarily for hypertrophy or strength!