Heavy bags have been around almost as long as combat sports such as boxing or Muay Thai have been around.  The use of heavy bags in ones training is one of the most important training methods and widely used by fighters everywhere.  The heavy bag gives the fighter many benefits in their development, such as power and conditioning.
Over the years, a wide variety of heavy bag types have been introduced to combat sports with various shapes and sizes.  There are the traditional heavy bags you hang from the ceiling, and punching bags that have a base you can set on the floor.  If you are just starting out, it can be confusing or difficult to know which one is best for you.
Traditional Heavy Bag
There are many benefits when training on a traditional heavy bag.  From my experience, they can be very heavy, and provide a lot of resistance and stability.  The resistance the bag generates will help fighters develop their explosive power and improve their overall conditioning.  These two traits are critical when going head to head with an opponent.
Heavy bags are built to withstand a lot of abuse and punishment, allowing them to last for years to come.     This will allow you to hit the bag as hard as you want without worrying about destroying your new bag.  Depending on the type of material your bag is made of, it will eventually rip or tear, but this will not happen for a very long time.  In the sixteen years of my training, I am only on my third bag.
As far as cost, the heavy bag is much more affordable than its counterpart.  It can cost less than one hundred dollars, and as much as three hundred to purchase a heavy bag.  The cost is based on weight, material, and retail location.  If you are just starting out on a heavy bag, purchasing a seventy pound bag that is under one hundred dollars is a wise choice as well as inexpensive.  The more advanced you become in your training, you will eventually upgrade to a heavier bag to maximize your potential.
There are some disadvantages to a hanging heavy bag, however.  They will require a place to hang it such as your ceiling or a heavy bag stand.  Heavy bag stands can cost upwards of one hundred dollars or more depending on the quality.  With a bag stand, you will need plenty of room such as a garage to store it.  If you hang it from a ceiling, you will have to buy a mounting kit to attach the bag to your ceiling rafters or your wall.  You also have to make sure you do not do permanent damage to the buildings infrastructure where the bag is being hung.
 Free Standing Bag
There are a variety of free standing bags, such as the wave master, and B.O.B., or Body Opponent Bag.  Depending on which one you choose, the advantages and disadvantages can vary slightly, but we will focus on them as a whole.
You do not need to buy any extra equipment such as mounting hardware or a stand.  This can save a lot of money when getting set up.  You can use this bag anywhere you want, even in your kitchen if you so choose.
The weight is comparable to a heavy bag, but easier to move.  A B.O.B., or body opponent bag, can weigh as much as 250lbs on its base.  With its weight base, is does provide some added resistance allowing you to develop your power and improve your conditioning.
The free standing bag does have some of the same benefits as the traditional heavy bag.  With some benefits, however, there are a few disadvantages to the free standing bag as well.
First, even though the bag weight is comparable to the traditional heavy bag, it cannot always take as much abuse as the traditional counterpart.  For a B.O.B., you are limited to the front and sides, not the back of the bag.  Hitting from behind will result in tears in the material.
For a more advanced fighter, it is likely you will knock the stand down, requiring you to pick it up again.  I can generate enough power to knock the bag down almost every time.  This will result in wasted time with your training.  And to prevent it, you will tend to hold back.
Second, the cost of a free standing bag is much more expensive.  To get a good quality bag, you are looking at spending at least two hundred dollars easily.  Pricing can be a huge factor when making a sound investment, and this cost can persuade you to think twice.
Finally, depending on the type of bag and the intensity of your training, the free standing bag material may not outlast the traditional bag as far as time and use.  Though these bags can have the capability to last as long as a traditional bag, it will depend on the type of intensity you dish out, and the quality of the material.
Conclusion
Anything you end up buying is always going to have both pros and cons.  The same is true when thinking about choosing a heavy bag to add to your training.  The best thing to think about before purchasing a heavy bag is to base it on what makes you feel more comfortable to invest in, and how much you are willing to spend.  The type of bag you choose to buy should also be based on your level of training, space, and convenience.  Ultimately, it is your preference on what you choose.  Either way, you will not be disappointed.