It might depend on your location and weather conditions, but I'll throw in my $0.02
I have a full plastic windshield and like it a lot for our weather in South Texas. I know it will be taken off in the summer because of the heat, and in the winter, I wanted it to keep the "icy" blast of 50deg wind out of my face when I'm out riding in December-February.
My buddy has a half windshield and it makes dust circulate in the cab. So does my full windshield. I figured I'd at least not have to duck behind a half windshield to get the protection if I'm going to deal with the dust.
I wouldn't pay too much for a windshield for precisely the reason mentioned above. They scratch easily and they are kinda cheesy when you think about it. It's just a piece of plexi-glass strapped between the roll cage. But the winter wind not in your face is nice.
I have not had any fogging issues, but mostly because I just don't ride if it is cold and rainy. And cold and rainy is anything mid 50s and below, Hahah!
I got my windshield
HERE
It's been working ok, but I'm about to put it away for the season barred we don't get another norther. These 70deg February days are super nice!