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Multiple vias are better, to a point. Redundancy saves your
yield in big designs or poor-via-yield processes.
However beware of field loading or metal uptake effects in
large via beds (> 2xN). The norm is sparse vias and this is
what the process has to be optimized for. The interior vias
of large beds then do not represent the tuned-for case and
their quality / yield can suffer.
Usually multiple vias are preferred specially where current density is high, you can use an array of 3x3 if wide metal is available, as depending on the foundry there are different rule for NxN array and single via. Consideration should be design area and the signal current density being affected.