If I really had to choose... Ben survives, Kaine dies. I'm a huge fan of Ben and after so many years he is finally back (well, he was destroyed by Dan Slott but Spider-Geddon fixed him).
In a perfect scenario, they both get to live. Nobody has to die. If Marvel doesn't know what to do with them, then... just leave them in limbo 'till the right person to use them arrives.
If there is several Spider-Men (Peter, Miles, Otto, Miguel), then why can't there be two Scarlet Spiders?