Just over a month ago, I traded my Panerai 118 for a Rolex GMT Master II (116710). Now, the 118 is a 44mm, and i know you're talking about the 40mm GMTs, but I have had both Panerai and Rolex now. I also once had the Omega Seamaster GMT. If you're concerned about looks over function, then it's purely up to the individual. Some people will prefer Rolex over all other watches, while others will prefer the Panerai. If it's flexibility with bracelet/strap, then either one will work, as you can easily wear the Rolex with leather or NATO straps when you want, and while with the Panerai it's the bracelet that would be the sometimes choice. If you look at functionality, then since we're speaking about GMTs and not time only or chronographs, then you can't really compete with the Rolex. The Rolex GMT movement is the original, and works the way someone traveling would want it to work (many other threads discussing the merits of this). If you want to talk about longevity, maintenance, and long-term appeal, then Rolex almost has to be the answer. There are millions out there, and they have been proven to be solid for decades. There is a huge parts supply, and Rolex Service Centers on every continent except Antarctica.