For me I don't like either as I want the full Android experience. I'd pick the Nexus over both of those and for most folk I send them back to the iPad.
I want to know which tablet is better overall here are the specs http://www.phonearena.com/phones/compare/Samsung-Galaxy-Tab-S2-9.7-inch,Sony-Xperia-Z4-Tablet/phones/9385,9264

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