. . . Swim trunks drive me absolutely insane, I cannot understand why anyone would prefer them over jammers or even whatever undies you wear day-to-day. But my main dive buddy wears trunks every single time, so YMMV.
As I mentioned above, I usually wear jammers. However, sometimes I resort to wearing trunks. Although lycra jammers are less body-hugging than lycra briefs (like the classic Speedo), I still find them a little too revealing to spend much time topside in them doing anything but waiting out a surface interval on a boat with my fellow divers who look just as goofy in whatever they are wearing. For instance, if I want to be able to walk off the boat and immediately walk back through town to my hotel or have a beer at a bar with my dive buddy, I'd rather be wearing swim trunks because they look and feel more like ordinary streetwear shorts. Some swim trunks are baggier and/or longer than others. Board shorts are baggy and long and therefore tend to bunch up uncomfortably, but there are others that I find useful in some circumstances.