This isnt a question about whose backhand was better since Federer clearly wins that category, or who has more variety which is also Federer since he can hit flat, topspin, and slice well. Im asking who you think was more aggressive off that wing in general. In my opinion, it was Pete. Sampras tried to pull the trigger on almost every occasion except imporant points. In his prime 04-06ish, Federer is content to hit the short slice to pull his opponent up and reserve his topspin backhand for passing shots and put aways. Now he hits over the ball more, which is part of the reason he is losing more.