Hi there,
As a long time photographer, I would suggest that you test both lenses prior to purchase, if possible. I have an F80 myself and I think it's a nice every-day type of camera, but I also think that you might consider spending a bit more for better optics. I am also a long time user of Nikkor lenses, so please forgive me, but I suggest that you check out the Nikkor 24-85 AFS-G and 24-120 AFS-G VR lenses. These are more expensive, but the improved optics should last you a long time and provide some very nice images. I don't know much about the Tamron lens, but the Nikkor 28-80 may not be the best choice based on reviews. In any event, at the end of the day it depends on what type of images you want to take. There are a lot of shooters in this forum who may have specific experience & opinions on these and other lenses, so look at what other users have to say. Good luck and good shooting!
Greg