Mostly this makes no sense because the things BGP cares about are orthogonal to mere IPv4 or IPv6 addressing.
But if there is a difference, IPv6 means less prefixes are needed for any given provider, since the IPv6 prefixes are huge and unfragmented, we can usually give a provider enough address space in their initial allocation to last them forever, and if they exceptionally out-grow it, the larger space is available, whereas with IPv4 there's no chance anybody can give you a /16 even if you warrant one.
But if there is a difference, IPv6 means less prefixes are needed for any given provider, since the IPv6 prefixes are huge and unfragmented, we can usually give a provider enough address space in their initial allocation to last them forever, and if they exceptionally out-grow it, the larger space is available, whereas with IPv4 there's no chance anybody can give you a /16 even if you warrant one.