Which key feels more comfortable on Attack Move Click?

I have it bound to Mouse 4. The mouse button that's usually used for "page down" in a browser.

Try left mouse button? I don't use attack move, but this way seems pretty viable.

I have it bound to my left mouse button, and have the ordinary left click function rebound to shift-left click.

The attack key, is simply about muscle movement, I much prefer 'attack player attack move' since it is the smart cast version if attack move, but that's just me, so far I've set mine to the A key leaving A for attack, S for stop, and D+F for summoners.

I've seen please use spacebar or even extra mouse buttons on the mouse key, whatever you choose it has to be something you're comfortable using, and accessing in the blink of an eye, without thinking about it.