The matching between Ch1 and Ch2 in the dual digital potentiometers is
typically 0.1-0.2% and we usually specify ±1% as a maximum. (These specs can be
found in the datasheets). This is dependant solely of the fabrication process.
I checked with the product line and there is no one digipot family or part that
has better performance over the others in this regard as they are all built on
the same process.
The ABSOLUTE resistance values of digital potentiometers vary over quite a
large range +/-20% is not uncommon. If the customer has any concerns with the
absolute resistance, they should consider one of the non-volatile memory
digipots such as AD5252:
The AD5252 features patented RAB tolerances storage in the nonvolatile memory.
The tolerance of each channel is stored in the memory during the factory
production and can be read by users at any time. The knowledge of the stored
tolerance, which is the average of RAB over all codes (see Figure 16), allows
users to predict RAB accurately. This feature is valuable for precision,
rheostat mode, and open-loop applications in which knowledge of absolute
resistance is critical.