Hi, it depends on your aims as photographer. For a professional use or a pretty demanding photographer, glass is always going to deliver better quality image, resolve flaring better, and it's more difficult to scratch it. However, it's heavier to transport and more expensive.
For just split shots, the bigger is the dome, the easier to take them, so if there is not a budget buy the biggest you can made by glass, and you will have some for decades. This way you will buy only once.
Regards.