The position next to the spacebar seems more awkward than to the left of "a", especially if you use Emacs or otherwise a lot of Ctrl presses. I currently have the CAPS key mapped so that it's Esc on tap, and Ctrl on hold. Works great.
It's only awkward next to the spacebar if you use the wrong finger. What key are you currently hitting with your left thumb? That is a whole finger you could be using to hit LALT key, instead of letting it just sit there wasted., and it's very natural. You can use Emacs easily with this configuration for both modifiers.
On a thinkpad keyboard, my thumbs fall naturally on the space bar (well, rather between the space bar and the left trackpoint button), so hitting the alt next to it implies an uncomfortable bending motion of my left thumb. Also, the x is just over that key, so doing M-x in Emacs would be a weird pinch-like move. Maybe it's a matter of habit, but using CAPS as Ctrl/Esc is literally a 2mm move of the pinky to the left from my home position.
