I don't think both of them are acceptable.
But, if I have to choose one, I would go with the newer security patches. And I ain't any celebrity or a high profile person.
I can understand why most would go with the newer OS. If you look at those security bulletins, those are not something which are highly exploited in the wild. All those new features are of more first hand importance to a lay man rather than say some boring security patches.
Don't get me wrong, I do care for both newer features and security and that's one of the reason that I use a Nexus!