The topper is the first thing people notice, so match its size to the tree. A 7 to 7.5 ft tree usually suits a topper around 10 to 14 inches tall, and remember to leave space between the topper and the ceiling.
Fit matters more than looks. Most toppers attach with a spiral or tube base that slides over the top branch. Check the base diameter against your tree's top tip, and choose a lighter topper for artificial trees with a thin top section, since heavy toppers lean or droop.
Lighted toppers come in three types: plug-in models that run a cord down the tree, battery-powered toppers, and toppers that connect to some pre-lit trees. Plug-in toppers are brightest; battery models avoid a visible cord. Check the weight before you buy.
Stars suit most trees, angels give a traditional feel, and large ribbon bows look good with matching ribbon on the branches. Coordinate the color with your ornament set.