There are advantages to doing both barbell bench press and dumbbell bench press. Barbell benches will allow you to lift more weight. But dumbells allow you to work each side of the chest independently and they incorporate more stabilizer muscles because you have to balance and stabilize two separate weights.
I personally include both variations in my workouts. For example, I may do barbell bench presses for a few weeks, then switch to dumbbell bench press for a few weeks. Iíll keep alternating between the two exercises.
Should I hire a personal trainer to help me with my workouts?";
I recommend that beginners hire a personal trainer to help them learn their way around the gym, show them how to use the equipment, teach them the basic exercises, proper exercise form, etc. This will save beginners a lot of time and frustration in the gym by helping them to avoiding most beginner workout mistakes.
But once a person knows the basics of working out, they really don't need a personal trainer to follow them around the gym and count their sets and reps for them. What they need at this stage is an experienced fitness consultant to help them track their progress and determine if what they are doing is working, and help them plan out their training and nutrition program so they can achieve their fitness goals.