The only thing that really works is grass. Anything else and you will be constantly on your knees with an old kitchen knife taking out weeds. You can grow clover or chamomile in the grass and maintenence can be done with a lawn mower. Moss also workd but you need shade and moisture for that.

You might want to try Mazus reptans. This grows so densely, providing it has adequate moisture, that it crowds out weeds effectively.

I would recommend Elphin Thyme. Hardier then other Thymes, denser and can take lots of foot traffic. I use it in all of my rock paths.

Check out "stepables". Different varieties of hardy foot traffic plants.

-S

I recommend Monkey Grass - Ophiopogan japonicus
. I have it growing between bricks in a walkway & it's proven to be very tough. It survives summers of 100 degree weather in the sun, needs only water and is oblivious to insects or disease. There are two "sizes" and two colors: green & black.
It's safe for USDA 8-11; Sunset zones 5-9, 14-31, warmer parts of 32

Here is a link that might be useful: monkey grass