Have always used the facility provided mats up until about a year ago?
One fitness club where I took Yoga had really old and run down matts so I ended up buying my own cheap mat, unfortunately it was too thick.
When I joined my new gym, they supplied fairly good mats, and since it was an upscale fitness club, members generally took good care of equipment and wiped down their mats after use.
In any case, when I did use one of their mats, I made sure to overlay my own towel on top of the mat, anywhere where my head, hands or face would get close to.
I bought my last mat, https://www.amazon.com/gp/product/B00DV4NMPC/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 after the ones at the gym were getting a little worn. Right as I bought my mat, the club replaced all of the existing mats.
Even with my own mat, I still make sure to put down a towel on top of it once I transition over to the seated or laying postures.
It is nice to know that the clubs provide the mat in case you forget your own, along with straps and blocks. (which I do not bring my own yoga blocks with me).
Eh, no need to waste so much money on a matt.
Plenty of really nice ones on Amazon.
Recently picked up this guy... and has been great.