The Best US meter to use

The most accurate Glucose Meter is the Contour Next. See https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5505415/ - see Table 2 for accuracy comparisons. See https://www.ascensiadiabetes.com/products/contour-next-gen/

I can't remember where I saw the data, but the One Touch Ultra was considered one of the more accurate meters several years ago. I have/had several of them. But these are not UK NHS issued and strips can be difficult to source here - plus when I worked out my newest one was over 7 years old (!) I decided its best years were over.
Currently using the NIPRO 4SURE Smart Duo as it can also measure blood ketones.