Even though tradition may try to tell you that glass is the most popular type of Christmas ornament, I would beg to differ. Growing up, and even now with kids of my own, I witness ornaments dropping from the Christmas tree on a regular basis, during the holidays. Even on carpet, glass ornaments can easily shatter, leaving a dangerous and costly mess.
As Vickerman's largest online reseller of Shatterproof Christmas Ornaments (made of plastic), we absolutely LOVE them and we rarely get returns from breakage and simply do not hear any complaints about the appearance. They have really mastered the art of making them in all sort of styles, from matte to glossy (glass-like) and even covered in glitter while maintaining an incredible durability. They make them all the way from tiny marble sized to massive ornaments many feet wide!
One note: You can sometimes see a seam (pictured below), but you have to look REALLY close but it is well worth it to have safety and not have to continually re-purchase your ornaments.
So, they are frequently cheaper than glass ornaments, they look JUST like the real thing, they include better UV protection and they just don't break easily. Don't believe me? Watch me drop some Shatterproof Ornaments below and judge for yourself: