Speaking of neither, but trying to be helpful: check out KnockoutJS. Just used it for a fairly complicated project for a client. Goddamned delightful. Perfect (read: not dogmatic) separation between markup and code. CoffeeScript + Jade templating + KnockoutJS = web app delight.
EDIT: Backbone/Spine target different use cases than KnockoutJS, but KnockoutJS seems to target the more relevant ones.
MVC - MVVM : grudgingly, I agree. I did a bunch of Rails coding, so my MVC is the Rails MVC (not the real MVC). KnockoutJS basically ignores Models, so sets off my Spidey-sense, but...
I haven't done much GUI programming, so I'm not familiar with the classic definition of MVC. KnockoutJS's MVVM (really V-VM) is very clear and I love it.
KnockoutJS would benefit from the addition of Models (in order to make it a 'framework'), but I'm 90% more productive right now and am certain that KnockoutJS will evolve to include Models.
EDIT: Backbone/Spine target different use cases than KnockoutJS, but KnockoutJS seems to target the more relevant ones.