The aquarium hobby is divided into many parts, but largely recognized are the two major groups: saltwater and freshwater. Those who don't understand them both well enough are often misled to believe that saltwater is better than freshwater, and that beginners keep and prefer fresh, while those who have had some experience move on or "graduate" to salt. There are many errors in these misconceptions, the first being that "saltwater" and "freshwater" are clear-cut definitions at all. There are countless aquatic habitats, ranging from virtually pure snow melt to briney salt lakes, and every degree in between. To dismiss brackish waters, mineral springs, dark acidic pools, hard alkyline lakes, and a host of other water types is to dismiss a rainbow of diversity in ecology. The second error is to think of one as being better than all the others. If you prefer one to another, that doesn't mean that someone else feels the same way. Many advanced hobbyists keep one or two saltwater tanks, if any, and consider their freshwater tanks to be their favorites.
To truly understand the diversity of aquatic environments, many hobbyists have begun keeping "biotope" or "geographic" aquariums. In these tanks, the hobbyist attempts to simulate a specific habitat. The fish, plants, gravel, decor, and even water are each important parts of these set-ups. Generally speaking, a "geographic" aquarium simply represents an environment, and the items added should appear natural and conform with that habitat. In a "biotope" aquarium, more care is given to be certain that not only does each item appear appropriate, but that it actually is authentic to that region. For instance, the wood that is used should be of a type that is native to that area, and the sand must be the correct type of mineral for that region. The same is true for the plants and fish, etc. Setting up a true biotope aquarium can be an extensive undertaking. A geographic aquarium is a bit easier, and still allows an understanding of the habitat. Both require knowledge of the water conditions, which the aquarist should attempt to simulate in these artificial environments.
A biotope is any piece of an environment that is unique to itself. Even within a small area, there are many smaller biotopes. An African rift lake, for instance, can have a littoral zone where water meets air on rocky shore, a rocky wall descending into the deep, a sandy bottom zone, the open water column, and a shallow sand bed with grasses all within the same lake. Likewise, with saltwater there are many different biotopes; a sunny lagoon, a reef face, a rocky coast, a tidepool, the open sea, a sandy bottom and countless others. Within any given geographic location there can be numerous individual biotopes. Even the time of year can cause the biotope to change beyond recognition, such as the flooded forests of the Amazon.
Once one begins to understand the care and planning that goes into creating any of the many different aquatic environments, it becomes rather pointless to think of one as being "better" than another.