A true master and student of baseball training will study the available methods, take the best, and form them into a comprehensive program. Even the most talented ballplayers need to continually develop core strength and conditioning, which is fundamental to an effective training regimen. Even though the need for a quality training program is universally recognized, there are few that deliver on the promise of improved performance.
Everyone who makes a living through baseball (or someday hopes to) is looking for that extra advantage that will make them stand out. Billions of dollars are spent each year on the newest, high-tech equipment, individual batting and pitching lessons and many different gadgets and gimmicks. The problem is everyone believes they are a training expert and most don't understand the first thing about proper baseball training methods.
This is obviously not what you want and need to improve your baseball performance. The program you choose should include methods that improve balance as well as strength: medicine ball drills, free weights and other dynamic movements are good examples. By approaching your workouts in a more "holistic" (or complete) manner your overall conditioning will improve at the best possible rate while honing your baseball specific muscle groups.
Be sure to stay away from machine-based training. Trying to do baseball strength training on machines is a complete waste of time. Worse actually, because it's taking time from more effecitive training. One problem with machines is that most of them require sitting, which is exactly opposite of what is done on the baseball field. Train on your feet so that your body is conditioned to respond while you are on your feet - not sitting.
With that said do not swing a heavy baseball bat or throw a heavy baseball. These baseball training methods will not improve your hitting and pitching. These techniques will severely affect your baseball hitting and pitching mechanics in a negative way and can even lead to injury!
To truly excel on the field, training must incorporate the specific movements involved in baseball. Movements in gym workouts should recruit the same joints, muscles and movements that are used in the course of practice or a game. Get this right and you will be the envy of your peers; get it wrong and you will never know how good you could have been.