Go for the MB/Sigla windshield, without a doubt. You can most certainly tell the difference between OEM and non-OEM. You will encounter problems with clarity and distortion in non-OEM glass. You are within your rights to expect original equipment materials when dealing with insurance cases.
FYI. Pilkington is good stuff. My Volvo has an OEM Pilkington windshield and it's very good quality. I've just never seen that brand in an MB. Sorry, I can't comment on the glare issue.