These days I do not use anything. One day on a long tour in a weight reducing purge I pitched the ground sheet and never looked back. I decided that groundsheets are just not necessary. I figure that I let the tent bottom take some abuse I can patch or recoat it as needed, which it turns out has been seldom. If it ever gets too bad I would start using a ground sheet after the bottom is beyond patching, but so far I have never had a tent bottom be the reason for replacing a tent. My take is that if I spend more money to get a lighter tent, the last thing I want to do is add the weight of a ground sheet or worse yet spend even more money to add the weight of a fancy footprint.

I have used Tyvek and plastic ground sheets in the past, but I have never used a manufactured "footprint". When I did use ground sheets, I always made them just a little (maybe 2") bigger than necessary and then folded the excess under so none showed.