The only decent tang in a real sword is the
full rat-tail tang. A sword with a half tang will most
likely have its handle snap when doing anything with it
other than holding, and a full tang without the rat-tail means
the hilt cannot be removed to inspect and clean the tang.
Note: Some swords are designed to only have
a half-tang, such as the Japanese katanas and family. However
these tend to be the exception rather than the rule.
A rat-tail tang, one which has a pommel attached to the end, means the entire handle can be removed, allowing the owner to oil both the blade and the tang. (A sword is no good if the tang rusts).
If you are buying a sword, ensure it has a full tang, and it is best to have a pommel that allows the handle to be removed.