Which lens is best for Nikon D5100? (Hurry)?

Which lens is best for Nikon D5100? 70-300/18-200/ or 18-270? My father likes to taking photos of nature.Price isn't matter. I want to know wihch is best.

(Please hurry, because we're planned to buy tomorrow.

Since you say price is no concern…
For animal shots in the Nikon lens range:
80-400mm (USD 2700)
200-400mm (USD 6700)
400mm (USD 9000)
600mm (USD 9800)

More affordable:
Sigma 50-500mm (USD 1500)
Sigma 150-500mm (USD 900)

For nature you will want a longer lens, so forget the 18-200. The 70-300mm VR is the best of the ones you mentioned - assuming it is the VR and not the cheap 70-300mm "G" lens. The cheap one won't autofocus on your D5100. You need the full VR version, which is quick to autofocus and the Extra Dispersion (ED) glass is top notch for the money. The only 18-270mm lens I know of is the Tamron, which is not particularly quick to focus - which may be a problem with nature pictures.

None of them are "best" it all depends on what range you (or your Father) wants.
If he wants the longest range then the 18 - 270 covers more than the 18 - 200 and almost covers the long end of the 70 - 300