with what you already have.. I'd take the 24-70mm.

It'd be nice to have a more general purpose one size fits all lens, and if that's your photographic methodology then you'll probably get better value from the 17-70.

I think once you've been shooting for long enough, you soon realise what it is that you really want, and at what focal length you want to work at!

FWIW: I'd take the faster aperture over the longer zoom ratio any day.