I would think it would depend on what he does for work, if he works with this hands like a mechanic and such I would go for the 10K or titanium or tungesten, if he doesnt really work with his hands then 14K or 18K
That is what I was going to say too; if they does any kind of work where his ring would get bumped or scratched a 10K might hold up better for him. If he does more computer work 14K would probably be fine.
I have trouble calling any alloy that has more alloy than gold "gold", so I'd pick palladium or silver - or tungsten, titanium over 10k. But that's just me.