Tetras come in all colors, shapes, sizes, and with all different charicteristics. For the most part Tetras are a very hardy and healthy fish and the Tetras in my tank have all survived for a great deal of time. I have several different kinds in my tank and I have grown to like a few certian types. My personal favorite is the Von Rio Tetra (Hyphessobrycon flammeus) for their activeness and for their nice orange colors. Von Rio's have been among the most active in the tank.
I have found that tetras are one of the best fish you can have in your tank. The tetras in my tank at the time of this writing are about 2 years old. I have only had 2 die. One of them died (I think) of some disease because it always jumped. One day the fish jumped out of the tank and on to the floor and wasn't found for a couple of months. The other tetra did very strangely. The fish somehow managed to swim through an empty plant holder and got stuck through the holes in it and died. I was unable to take the fish out of it so I had to flush the fish and the holder. The holder was only a thin plastic thing for potted plants.
Many retailers have quite a collection of Tetra's because of their abundance and popularity. Remember, if your fish retailer doesn't have a kind you are looking for the will often be happy to find some for you and order them if needed. Most retailers would be happy to order any kind of fish or plant you would be interested in to keep your business.
Tetra's are usually mid-tank-feeders and are usually active during the day. They go well in many community tanks and are easy to manage. They are also good for starting a new tank because they are so hardy and live in a variety of water conditions which are benificial to new fishkeepers as well.
In my experience with many types of Tetra's I have concluded that Tetras of all kinds are active and inaggressive fish that go well in a variety of setups. It is neat to watch these interesting and beautiful fish and is a nice addition to any freshwater tank.