Privacy Glass = darker glass typically against rear windows, provides no UV protection
Aftermarket 'Tint' = darkens any window of choice and provides UV protection. The darker (lower percentage), the more UV protection.
As previously stated, get a quality brand and installer. Cheaper is NOT better, something like Formula One tint is way better...choice of regular versus Ceramic, etc. Also, you will definitely need to factor in glass that have built in radio antennas.
I have done 50% windshield for some kind of UV protection against dash, 35% all around including the privacy glass, and 35% against the moonroof.
Good luck!