I know this is going to generate significant antagonism for me from this group. However, my pet peeve is carry-on.
On a flight from ATL to DCA last week, my up-front seat mate was a woman who had turned her "carry-on" bag sideways under the seat in front of us, taking up all of the space. I had to ask her to turn it so that I could get my briefcase (the only thing I normally carry on) under the seat in front of me. She reluctantly did that. Then, when we had landed, she spent what seemed like hours getting another, larger bag out of the overhead. She was also carrying a purse; so she was violating Delta's "two carry-on" rule. I know that most of you carry on everything you plan to use on the trip. I just think you ought to check it. In over forty years of flying, I've never lost a bag. The closest I ever came was at DFW, when they sent it to the wrong carousel. That cost me 20 minutes. And I check stuff that I COULD carry on.
The bottom line, from my view (which is probably going to differ from most of yours) is this:
You don't really gain much from carrying your bags on board. In fact, you may lose, since you have to sweat from the carrying, especially if you have connections.
If you check your bags, (and especially if you're an elite member on Delta) they'll be first on the baggage claim conveyor.
You don't have to worry about people like me cussing you (usually not out loud) when you try to stuff that too-large "carry-on" in the overhead bin.
You're safer. The less stuff there is in those overheads, the less stuff there is to fall on your head if there's an accident.
I could go on and on, but I've had my say.