Will muscles gained by growth hormone be more permanent than muscles gained by using steroids?
Short answer
Steroids + physical activity generally increase your muscle cells in size. Growth hormone + physical activity increases the muscle cells in size and multiplies them by promoting growth of new ones.
No matter how you gained your muscle mass, your body will always do it's best to match the muscle mass to your physical activity levels. The harder/longer your physical activity, the bigger/stronger/faster your muscles will be. When you reduce your physical strain, the muscle mass will gradually be reduced to match it.
Long answer
Human body is a highly adaptive, energy efficient "machine" it is designed to sustain only as much muscle as is needed for each individual's daily physical strain. A person used to doing heavy physical work (lumberjack, athlete, etc) will have much bigger muscle mass compared to non physically active individuals. Should an active person reduce his daily physcal strain his body will gradually adapt by reducing the excess muscle mass - so as not to feed and carry it around if it's not needed.
The same works the other way around - if a physically inactive individual starts going to the gym on a regular basis his body will gradually adapt to the new hardship by growing more muscle mass in order cope with the person pysical activity level.
The speed and intensivity of the muscle building process is increased by introducing steroids or human growth hormone. Steroids rapidly inflate the existing muscle cells with protein and water while growth hormone stimulates growth of new muscle cells in addition to inflating the existing ones.
No matter if muscle mass was gained with the help of steroids, human growth hormone or hard work alone, the body will reduce it if it's no longer needed. In theory HGH users should retain more muscle mass because of the increase in quantity of muscle cells, but don't count on anyone noticing it:) If your physical activity goes down, so will your muscles - no matter how they were gained.
Muscle memory
On the positive note there is such a thing as "muscle memory". Once the muscle mass is developed, even if it gets reduced due to inactivity, it will rapidly get restored should the activity levels increase again. A person starting to build muscle mass from zero might have to spend years to reach the bodybuilding type phisique, while a veteran bodybuilder who hasn't been working out for years can get into top shape within a few months of hard work (or a few weeks weeks with HGH and steroids).
In addition to energy efficiency the body has another aesthetically undesirable inclination - to store energy (fat) and thus keep you prepared for potential bad times (periods of famine) which may or may not come.
The human body doesn't care about fashion. We may want to look muscular with next to zero body fat, but the body is only interested in functioning efficiently. Why drive through the city centre with a trailer truck and almost empty tank of gas, when a motorbike with a full tank of gas will allow you to drive easier, faster and longer. The body aims to remove all unnecessary muscle and save as much fat as possible (to prevent you from starving if you run into hard times). It is exactly the opposite of what we desire:)
If you want to prevent your body from removing the excess muscle mass, you have to use it - stay active and work out on a regular basis. If you want to prevent your body from storing fat, you have to show it that food is always in abundance - eat small (protein rich, low carb) meals, many times per day.
