Of the two? There are a number of VSA center speakers.
Like a previous poster, I would recommend staying within the VSA family to keep the speakers' voicing consistent. If there weren't VSA center speakers available, that would be a different story. You wouldn't buy a left and right speaker from different companies would you?
In all things audio, synergy is everything. Sticking with the same speaker company is one pretty safe way to have synergy.
It may well be that the Selah offers better horizontal coverage, but that is just one factor among many in speaker selection.