Both the bench press and dip exercises add strength, definition and muscle mass to your upper body. The bench press is a fundamental compound movement that works your chest, shoulder and triceps muscles. Dips also recruit the triceps and shoulder muscles, but don't focus on your chest as much. Ultimately, choosing between the two exercises comes down to which muscles you most want to target.
Get Your Priorities Straight
If you want to develop muscle size and strength in the upper body, the bench press is optimal. This movement recruits multiple muscle groups and allows you to use a heavy weight, which promotes hypertrophy, or muscle growth. Dips are more appropriate for strengthening your lower chest and triceps, or building the strength you need to perform similar movements in a sport or job.
Bench Press and Dip Variations
You can alter your bench press form to tweak which muscles bear the brunt of the effort. Grasping the bar with a shoulder-width grip places greater emphasis on the chest muscles. If you want to target your triceps maintain a narrow grip, keeping your arms close to the body while you press.
You can also adjust your dip form to tweak muscle focus. Lean your body forward during dips to place greater tension on the chest muscles. To isolate the triceps muscles, keep your body straight while doing dips.
Beginners Should Use Spotters
If you're just getting started with free weight exercises, ask an experienced friend or trainer to walk you through proper bench press form -- then give you a spot to help you keep the weight under control. If you don't have a spotter, you can use a self-spotting Smith machine for bench presses.
Performing dips does not require a spotter but you might have to use an assisted dip machine if you lack the upper body strength to lift yourself.
Experience Level Matters
Because dips place a great deal of stress on your shoulders, you need sufficient upper body strength to properly perform the exercise. Advanced athletes can do weighted dips with a belt, adding greater resistance which promotes hypertrophy.
If you're just getting started with the bench press, you might not need to add any weight plates to the bar at all. Stick with the naked bar until you've mastered the movement, then slowly add weight plates until you find a level that's challenging, but still doable with good form.