If I were to judge by the types of vintage tree toppers that I find most frequently, I would have to give the prize to angels, followed by stars and then by glass finials. I found some of the traditions behind this in my on-line search.
Apparently early German Christmas trees were decorated with angels representing the host of angels that heralded the birth of Christ. In 18th-century Germany, tree-topping Christmas angels were formed of plaster on a composition armature, with paper robes covered in brass foil. Some late-19th-century Nuremberg angels wore paper-and-foil crowns, while others were backed by pleated paper wings and wrapped in matching paper skirts. In the United States, in the 20th century, a particularly popular angel tree-topper was manufactured by companies such as National Tinsel of Wisconsin and TIMCO. Made of lithographed and foiled paper, with spun cotton for clouds, these angels were backed by halos of hair-thin glass rods, which obviously broke easily, making them scarce today.
Stars also have a Christian meaning, representing the Star of Bethlehem that led the wise men to Bethlehem and revealed the birth of Christ. The star is also a symbol of light. I find that early star treetoppers are more frequently lighted and decorated with elaborate tinsel and foil.
The glass finial, or French “cimier oriental”, seems to be an offshoot of the glassblowing art of Christmas ornaments. Finials are often hand blown with single, double or triple ball designs. The peak is sometimes narrow and sometimes wider with a plunge design. Mold blown glass finials have taken more elaborate forms in the latter half of the 20th century with santas or other figures molded into the design.
Modern tree toppers are often designed to accompany a theme with many different styles available. One can find popular cartoon characters, famous people or sports teams. An elaborate fabric bow is sometimes used as a simple topping for a color themed tree. Many Christmas tree toppers incorporate lights of varying kinds. These lights may blink or not, and can be found in simple white or in any color that other Christmas lights come in. Light-emitting diode (LED) tree toppers are also available. Some toppers are battery powered, while others require electric current. Tree toppers are also made from almost any material, including plastic, metal, and fabric. Tree toppers are often found in silver or gold, although red is another widely used color. Some of the fabric toppers incorporate wire for flexibility and positioning.