I prefer dips to bench myself, although both are excellent lifts. Obviously if powerlifting is your goal you'd want to stick to the bench press primarily. Ultimately [no matter the goal] you'd use both lifts, but I don't see any problem with alternating them like you are doing.
Here's a quote from Dr. Ken..
"Contrary to popular belief the bench press is not a very good exercise for the development of the pectoral muscles. It is fairly good for the development of the anterior deltoid and triceps, but the standing press develops these muscles as well or better (better being defined as more quickly, more directly, with the production of more power or work during an actual repetition of the exercise), as does the parallel bar dip. However, if you care to do bench presses or presses behind the neck in a standing position, feel free to do so. Perhaps you can alternate pressing movements every few weeks, every few workouts, every other workout. You will never suffer from lack of variety." - Dr. Ken Leistner