One thing I see right off the bat are that some of these have very different watering requirements.

Elfin Thyme likes to stay pretty dry, while Irish Moss prefers moderate water, and the Scotch Moss likes it downright moist.

Also some sun preference differences. Elfin Thyme likes full sun, while that Scotch Moss prefers light to moderate shade.

So I guess the real question is, what are you growing in the bed as the primary plant, what kind of sun/water requirements do they have? If you're growing cacti in sand, that Scotch Moss isn't going to be happy, while the Elfin Thyme isn't going to be happy if you're putting it under heavy bushes/trees.

I've actually got a large swath and I'm thinking of sections of different kinds. One area is sunny and drier but it curves into a shadier and lower (wetter) area. So, theoretically, they all would work to some extent. The beds are mixed perennial, shrub, and roses...lots of roses (shrubby kind). I also have raised beds which are mulched around and I'm tired of having to weed the walkways and though introducing different groundcovers would be a good way to go, but I need something that can take a bit of traffic (not a lot, just a bit).

Well, the elfin thyme will withstand light foot traffic pretty well. The leaves and stems are very small but still surprisingly springy and woody so you'd really have to grind your heals in to seriously hurt that stuff. It is also likely the shortest growing of all those, so it should do pretty well as a boarder with the thicker stuff deeper in.

I planted creeping Mazus by accident last yr and I love it. Very low growing. Forms a thick mat. No problems with walking on it even with my kids and dogs! Very dense for sure and spreads nicely. I had it in full sun with no problems (zone 6-CT) but I think they recommend part sun-shade.