Well both and neither of course.
They are two different viewpoints of the actual underlying 4D Global Temperature Field.
They approximate it from two different directions.
Both end up being remarkably close to agreement over their entire overlap period.
That differences still exist should come as no surprise. Each should inform the other. Not fight as at present.
P.S. Being in a quasi-chaotic turbulent boundary layer at 2m rather than the more laminar layers the satellite sees will always require some assumptions.