I have the
tiles from VEX.
These tiles are thicker than the ones you normally find at Home Depot, etc. That makes them more resistant to people tearing the fingers off when they take the field apart.
When you shop you should look at the single "key" along each edge. On some tiles the key goes left, others it goes right. It's designed to keep you from getting some tiles wrong way up. But it has the unintended consequence of making some tile sets not interchangeable. For example, Home Depot tiles don't work with the ones from BJ's. So when you get the tile set, get a few extras ones. The VEX set comes with 4 extra gray tiles.