I’d have to see your whole roster to know for sure. My personal choice at first glance would be save it, followed by Spidey 2099. Jinx
More details would help us advise better:Do you run recoil masteries?Are you talking 5* or 6*?What kind of Sig stone haul do you have to throw into them?Personally, whilst they're both good champions, if you were talking a 6* Generic Gem, I wouldn't give it to either of them.
I'd hesitate to use the gem on either, unless you desperately need someone big, green and poison immune.Mr Negative is Nullify immune, has amazing utility and tbh would be a better place to spend a Gem.Why not spend some time on @BitterSteel 's YouTube channel, play around with Negative and see if he does what you need?