Tmaron 18-270mm or tamron 70-300mm?

I have been using the kit lens (18-55mm) that came with my nikon D3100, and now i think its time to change to a bigger one.
i made some research on the internet and i found 2 lens that I'm interested in.
the first one is the tamron 18-270 with this great focal length i can use it in almost any situation.
The other one is the tmaron 70-300mm i found that the image quality are a bit better with this one, however if i chose it, i would have to carry my 18-55mm every where.
in addition the information i got are not very specific and ill be thankful if someone could help me with this decision.

There are those who want a single lens solution to their photography and for that a lens like the Nikkor 18-200 mm or new 18-300 mm is a possibility.

If your budget is pinched, then lenses in that focal length range made by Sigma and Tamron may be your other choice.

It won't hurt you to carry an extra lens around with you.
In the "old days" before super zooms, we used to carry a body and 3 or 4 lenses; plus a flash and tripod!