I would have to go with the ring as long as it comes with a battery or maybe infinite power, kinda like the web shooters being infinite. The gem would be cool but apart from the whole servant of Cyttorak thing, what happens if like Cain you get stuck in cement. The symbiote would definately take over or possibly leave you halfway through a web swing. But unless the symbiote is Venom or an offspring of Venom then your screwed cause the original symbiotes used hosts up. No for me its gotta be the ring. Though if the Batmobile was on the list I would go with that. It might not really give you any powers, have you getting chased by cops constantly and being a huge gas guzzler. But damn is it cool.