Given that the paralleled caps would presumably be similar in design, I'm not sure that using dissimilar values would make any difference compared to using values that are close to each other. But my instinct would be to use values that are as close as possible, because doing that keeps the higher of the two values as low as possible. Everything else being equal, a cap having higher capacitance can be expected to have higher stray inductance, which would be undesirable if the difference were significant in degree.
Regards,
-- Al
In case of parallel caps you'll simply have larger tolerance.I respectfully disagree. For example, 6uf +/-10% in parallel with 7uf +/-10% = 13uf +/-10%.
Regards,
-- Al