Blizzard has stated that the items we can make via professions were not intended to replace those dropped by mobs. So mob drops will always, over all, be better than what we can make. This is the reason many people are dissatisfied with production professions that make weapons and armor. But it’s not that simple. It never is.
It doesn’t mater how good dropped items are if you can’t get your hands on them. Some people are not members of large guilds. Some people don’t run instances very often. Some people don’t have a lot of money to spend in the auction house. The ability to make your own weapons and/or armor can be very useful for any of these people. And some people simply enjoy making things. I happen to fall into that group, as well as some of the others. So whether or not production professions are worth doing is very much a question of play style.
For those whose only reason for practicing a profession is to make money, then two gathering professions is most likely the best choice, such as skinning and mining. Again, it’s a mater of play style. Choose whatever works best for you.