Any anglo accent should be fine, and perhaps also a light Russian one. (Data points are Patrick Collison and an unnamed Russian founder.) Best? Perhaps Estuary English, but only PG has data to back this up.
"In the debate that surrounded a 1993 article about Estuary English, a London businessman claimed that Received Pronunciation was perceived as unfriendly, so Estuary English was now preferred for commercial purposes."
David Crystal, "The Cambridge Encyclopedia of the English Language", p.327
The smartest founder of all should be able to precisely adjust his accent for maximum karma.