DLC is a coating that should make the Titanium harder to scratch. Titanium itself is not super hard so it will scratch more easily. Beside that, the most apparent difference is the colour. The Titanium bezel comes in "natural" (plain titanium) while the DLC coating has a colour.
I don't know which one is better. The plain titanium scratches more easily, but on the other hand, a scratch will barely be visible compared to when you scratch your DLC coating, where you will see the lighter coloured plain titanium shining through the dark coating.
If the price is not relevant, I would go for the one that looks better for you.
