I think width is more important.
Width of what?
Shopping carts? Telephone poles? Airline seats?
No, I don’t think the width of a shopping cart is more important. I need to scoot the cart between the parked cars so I can return it to the cart bay thingie, and if it’s too wide that’s hard to do.
I think telephone poles are better being longer (higher). Not that I want them to be as narrow as twigs, but I think they should be pretty long.
I’d prefer airline seats to be a little wider. Not all of us are petite delicate flowers. Besides, what’s the point of having a really long airline seat?
Come on, yosemitebabe. Y’know it’s not the size of the shopping cart-it’s how you use it. 
Maybe it’s the motion of forward motion in the aisle, unless you have a broken caster.
Heh. You must use one of those sissy little hand-baskets.
A deep shopping cart is the best. That way you fill 'er up and the hands naturally go where they need to.
Just don’t pick up one of those old, beat-up ones that just kind of stutter around until the wheels fall off.
Silly nisobar, thinking in three dimensions.
Clearly, time is the most important. Followed by width times height, and then length.
Neither
The most important factor is distance along the 4th w axis of a 4 spacial dimensional hyper-penis.
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The most important factor is distance along the 4th w axis of a 4 spacial dimensional hyper-penis.