The results were quite dismal (the best effort is below), so I am not even going to ask what I did wrong.
Ok, but I will play the dumb guy and ask. What about this picture did you not like? It is tough to give advice unless we know what you were really intending for your shot.
You shot this at f8 with 1/125th. That's not too bad. F8 gives you a bit of DOF leeway for when the Hummer zips sideways (which they always seem to do). 1/125 gives you a nice wing blur but seemed to keep the head pretty sharp. Not every BIF needs to be razor sharp.
Did you try cropping this in post to get rid of some of the distractions to the left?
If this is your idea of "dismal", you and I ain't in the same league. A little cropping and some post (you *did* shoot this in RAW didn't ya?) and you would have a nice picture of a hummer. Nonone is gonna pay you a million dollars for it, but it is a pretty good picture.
Keep in mind, this was truly a "snap shot". I think you did pretty good with the time you had. One thing to keep in mind is that hummers often come back to the same group of flowers after darting away. That might give you some more set up time.
Me thinks you are beating yourself up a little too much on this one.
i did it for you...looks pretty good to me.