Sigma 18-250mm F3.5-6.3 DC OS HSM for my Nikon D5100?

Walk around-lens for a Nikon D5100, what do you think?

It's fine for an all-in-one solution

a better quality lens would be the Nikon 18-200mm or 28-300mm.

Nikon is much more into quality lenses than is Sigma. When you see that the Sigma lens is say
$200 less than the Nikon lens there's a reason for that - cheaper glass, less all around quality and
far less on the workmanship side. If you want cheap that's what you'll get.

It should be fine but I would get the Nikkor 18~200mm instead.