I've done both, prefer the carry on. I get a cheap backpack rain cover off Amazon, Inflator and MAV come off the shoulders and go across the top under the rain cover. I've shipped tanks ahead to be filled and ready to go when I get there, this was domestic and saved a day of getting them filled. Show up, pick up the tanks, go dive. On the way home I emptied the tanks and removed the valves, put them back on the rEvo as part of the carry on.
I upgraded the seat to be sure I was on the plane early enough to get an overhead bin. I would even check what planes were used on what legs and what overhead bin space they have. Give yourself extra time through security, they will pull it aside and look at it. I do call it scuba gear, advanced, new style. When discussing the scrubber, I just call it a filter. Filters out the CO2. Keep it very simple, but still accurate to the questions asked.