I got the heaviest, 18oz matte vinyl. It lays flat within a few minutes of being unrolled.
Turn around time was less than two weeks, and double-sided, 3' x 3' mat came in at under $35 shipped. I think it looks better than most mats purpose-made for space gaming, because it uses actual images of space. Both the Hubble and European Southern Observatory websites have excellent images free to download.
I used a colorful picture of the Orion Nebula for one side. I wanted the other side to be more muted, more of a generic starscape.