I have the first green 18X24 mat I ever bought, probably in the 70's, when they first came out in abundance. Can't even see the brand name any more. It had a coffee cup warp in it which I fixed by 90% in the sun on concrete with the glass on it. It's has a corner missing and some cracks on the edges, but it still works. It's in the bath tub right now, soaking! LOL
My newest one is an Omnigrid 24 X36. I think it works fine right now, but is less than a year old. We'll see.
I have a 30X36 white Dritz. Useless! I use it as a table protector on my dinning table when I want to sew there.
My Fiskars 5X18 I take to classes to use only in emergencies. Usually the teacher has a nice mat for us to use.
I recently bought a spinning Fiskars mat, which I have seldom used. I just got used to turning the blocks after the first two cuts, and old habits are hard to break.