Using a coaster prevents those horrific rings from showing up on your table, and can sometimes be interesting conversation pieces. While they are quite useful, they can also be rather annoying. Flimsy coasters will stick to the bottom of your drink, and spill water droplets when you try and peel it off.
While you could always go for a heavier coaster like a polished stone that will definitely stay on the table, you will be faced with a different problem. If too much condensation collects on top of it, or if you even move your drink around, you can count on water getting on your table top anyway. This is why the Concrete Coaster seems to be a step above either of the two aforementioned options. It is made out of concrete that is mixed with non-toxic ash that makes it super water absorbent. It’s heavy enough that it won’t slide around on the table or get stuck to your glass, and it will suck up any condensation your glass tries to ruin your table with. While these do have amazing qualities, they are a bit too expensive at about $12 a pop.