I have both!
Clay clothes are very easy to use, convenient and can be washed/reused, but in my experience it doesn't do as good a job as the clay bar.
Bilt Hamber clay bar has been my preferred option for some years. It comes in 3 grades, hard, medium and soft. Having used them all, I prefer the soft, since my car are kept clean and don't get too dirty before re-washing.
The clay bar is my preferred choice for the 6 month detail and re-wax (I use hard clay on friends cars which haven't had the same level of care and attention). The cloth is good for interim washes to get light contamination off the car.
As mentioned, it always amazes me how much muck you take off a clean car. Remember if you prepping the paintwork for refinishing that you want to take as much of the contamination off the car before you clay. This means washing, detar, fallout removal before you finish prepping the paintwork.
Also ensure you then have time to apply the polish/glaze/wax/sealant of your choice to prevent damaging the virgin paintwork when you head out on the road.
Take your time and enjoy.
regards, Neil