Well hell, I'll gladly grant the ST its aesthetics - I'd agree that at first glance the ST had 'radder' looks than the A500. It's more about the computer system (hardware) design; no floppy, no thought of expansion (the A500 had two buses etc), basically the A500 had a much more sound and thought-through system design, so it was more useful out of the box.
When I switched to an A500, it was a distinct step-up in manufacturing quality. I was glad to not have a separate floppy as big as a C-64 one, and I was relieved at being able to type on a keyboard that was designed by someone who designs keyboards, and I was especially relieved at getting rid of the rad looking F-keys
It was a key point for me, it was a definite step down from the keyboards of most of my earlier and lower cost home computers in design, feel and quality (clunk clunk plick plick two keys at once twice every minute). Very strange, especially since Atari has made some nice keyboards in the past.
Also, I liked the looks of the A500 when you watched the monitor - it had the most professional look and feel of all OSes I'd tried, all categories. Quite like the Mac, not as wonderfully cute, but much more feature-rich and usable.