So, my opinion is that for tournaments, we should use displacement. That will ALWAYS tell what fish is bigger. We don't really have that tech yet, so for now, mass will have to work. I wish they'd start measuring weight in tournaments in a tank. It's pretty simple, Newton's laws apply, even if they're underwater, just zero out the tank before adding the fish. Mass is mass (meaning weight) and the weight will show, and they fish won't be flopping around in a basket, and you won't have the issue of extra water being weighed as well. They do this in many college level tournaments.
That said, I do a few online tournaments, through TourneyX. They all use length. I have a bump board for this. If it's a beast, I'll weigh it too. The thing to keep in mind, is be prepared. In my boat, I unhook the fish, put a cull tag on it, which prevents unnecessary handling when getting the fish out of the livewell. Then I prepare my measuring device, and camera. get the fish, weigh it, snap a pic, and return it to the water. In the kayak, the process is similar, except I use a cull tag attached to a retractable tether made by T-Reigns. The fish is on the tether, and in the water near the boat.
I suppose others would be interested in girth measurements, along with length and weight, but I'm not interested enough to do it.
The point is, I do not have the fish out of the water for more than 30-45 seconds. You keep your fish out of the water for more than a minute, you might as well release it into hot oil. Out of the water time is a bigger killer than any livewell, handling, "breading the fish" in the dirt on shore, or even prolonged playing the fish out. Remember, the second that fish is out of the water, the clock is ticking. Try this, run a 100 yard dash, then hold your breath for a minute or more. Tell me how you feel after...