We travel with a set of Delsey Heliums (two carry on, a large trip, and an extended trip size) and a one-off Tusi Vapor suitcase and absolutely love them. They're all "hard (rigid) sided" 100% polycarbonate external shell, so for the size they are ultra light and all have durable 4-point rollers so you can stuff them full of gear and still get them around without issue. The carry-ons are international standard size, so no issues placing it overhead regardless of where we are headed. Load them up wet and the worst case is you have to open them and let the nylon liner dry out when you get home. No rust. Also very water resistant if it is raining when the plane is being loaded. Just wipe it down with a napkin or towel. There is nothing worse than soaking wet canvas luggage when you're traveling. We've been using this set for 6 years now and they are virtually indestructible. One has a crease on the corner where a handler must have slammed it to the ground, but it popped right out.
In the largest extended trip suitcase, we can pack our two BCDs (Hollis SMS75 and a Hollis LTS), both sets of fins, dive skins, one collapsed mesh divebag, mask, snorkels, and depending on my BC setup, one or two wreck reels. We're consistently 49-51lbs at the skycap stand. (In all our domestic US travels, I have found the skycaps at curbside check in will consistently turn a blind eye up to 55# for a $10 tip if I hold it visibly in my hand so they see it as I put the heavy bag first on the scale for them. Actual ticket counter reps don't seem to have as much of a sense of humor and will make me redistribute everything to within a tenth of a pound.)
I carry three reg sets and computers in a (at my wife's insistence) bright hot pink Stahlsac bag which I then place inside my carryon suitcase along with my DSLR camera bag and laptop on top. If needed I can create space by easily pulling out either the regs or the camera equipment as a "personal item" (or if bin space is full I can pull the regs out and gate check the carryon).
I've seen carbon fiber suitcases that are "super ultralight" that might allow us to squeeze an extra few pounds in, but I have a hard time spending that much for luggage that is designed to get banged up.
