I purchased the Sigma 24-70/2.8 about a year ago. I shoot a lot with this lens, it's my goto if I don't need a lot of reach. I think the range it covers is very useful. I'm sure the Nikon is even better in terms of IQ.
FWIW, the only lens I regret buying is the Nikon 50mm/1.8G; while it produces very good images indeed, I just never use it, it just seems like I need the flexibility of the zoom for my shooting.