As others have said, there are two main camps here: those who check everything but the fragile and sensitive stuff, and those who pack everything in their carry-on. I have always been in the latter camp, but is certainly nice to not have to lug a heavy pack through various airports.
The rate of baggage losses and delays has dropped dramatically in recent years. The main thing to be on the lookout for when booking travel is the connection time. If it is tight, there is a much higher chance of your bag being delayed. For many destinations, that means you won't have your gear for your first day of diving since there may not be a later flight coming in on the day you arrive. So if you have a tight connection to make, be sure to pack as much as you can in your carry-on.