Chaucey,
Your two shots were a good example of a shot that was quite soft and one that was markedly sharper.
I'm not sure why you've encountered some implied criticism as if you are being overly picky regarding these two shots. It should be a no-brainer that if you were comparing the two, you would reject the soft one.
Why was one softer than the other? It's hard to say. How do you ensure acceptible sharpness? Well, in a static scene such as what you displayed, you did the right thing -- take multiple exposures, re-activating the AF so that a possible miss could be corrected. When you're dealing with dynamic subjects, such as wildlife or cars or airplanes or people on the move, you generaly use AI Servo and one of your continuous modes, then compare at your desktop.
But, there is a difference between reasonably sharp and noticeably soft. There would have to be a compelling reason to choose a soft pic over a sharper pic. Sure, there is some creative leeway, especially if a somewhat soft pic has some great compositional elements that you couldn't get sharper. And, some pics that are somewhat soft when you view them at 100% come out looking great at Web size or printed at, say, 8x10. That's fine, but that doesn't imply that they're just as acceptable IQ-wise as the sharper pic. It just means that they can be used in a limited way and are good in ways other than the sharpness factor. The limitations are obvious -- if you want to make a larger print or print a close crop of the softer pic, well, not so good.
There's nothing wrong with looking closely at your images and aspiring to get the best IQ that you can, as long as you're actually getting out, taking pics, and learning as you go!
I've been having a time over the past couple of weeks -- I've been going to a local airfield and practicing shooting small planes as they take off and land. It's easy to get shots at a high shutter speed, but the "effective" approach is to pan along with the plane and shoot at a low shutter speed so that motion blur shows up in the foreground/background but the actual plane is in focus. Now, just imagine how the "keeper/failure rate" comes out when you're learning that skill, hand-holding a hefty telephoto lens?



