Gold, all of it.
On another note I thought it was interesting that when Han said "There's too much Vader in him," that Leia didn't counter him. Instead she replied "That's why I sent him to train with Luke." Pretty interesting. So Ben was a bad messed up dude from the get go and he was sent to Luke with the hopes that his guidance would be a rehabilitative Jedi military school of sorts. And if Snoke got to him *before* his Jedi training as Leia indicated then Luke wasn't to blame for giving powers to a psycho. Obviously they were already there given that Snoke is a Force user and was manipulating Ben. Luke just tried to turn him around.
I'm assuming that Luke's failure was in underestimating just how far gone Ben already was. Leia's failure "that's when I lost you both" was in sending Ben off with Luke instead of his dad. Obviously she tried to correct her mistake but unfortunately it was too little too late.