The Tamron has a significantly wider 24mm setting. the difference between a 24mm and a 28mm lens is significant. The Tamron also has VC. The Nikon was very large, very heavy, and is now pretty old, perhaps 18 years old or more on early run examples of the 28-70 AF-S. Optically, I expect that the Tamron is better...their G2 series is getting rave reviews, from people who are pretty Nikon-centric. Honestly...I always thought the 28-70/2.8 was ridiculously heavy and overly-large and obnoxious...
Have you owned a honking, 44-ounce, coffee-can-sized lens like this before? I find equipment like that to be...obnoxiously large and interfering in many,many situations. There are smaller,lighter, less-obtrusive options available.
I think many things shot with short lenses like the 24 to 70mm range focal lengths, when shot at f/2.8 look, like crap. So, there's that too. if one _needs_ to shoot at f/2.8....then one needs to do so. But...today we have decent,usable ISO levels that make an f/4 lens workable, often at f/4.5 or f/4.8 or even at f/5.6.