Thickness refers to the depth or height of the watch case itself. A thick case may feel heavier and bulkier, compared to thinner ones, as thicker cases are typically used for watches that have a higher water resistance. So it depends on what you would like to be able to use your watch for, for example; if you would like an everyday watch, we would recommend choosing a watch with a higher water resistance, therefore one with a potentially thicker case; or if you would like a more formal/dress occasion watch, then a slimmer case would be suitable.