Best Travel lens !!

Great question! I've never found the right answer either...here's what I've tried:

18-70 - great lens for the price, decent quality and not heavy but slow aperture.

18-200 - unbeatable versatility at the expense of sharpness. Most of my travel pics over the years were taken with this lens. I've used both the I and II versions but I've been looking for a change as I don't think this lens is good enough for the 12meg sensor on the D90/D300 (it was fine on my old D70).

Sigma 50-150 (version I) - spectacularly good lens for the price. Wonderful for portraits and much smaller than a 70-200 f2.8. The speed is very handy in lower light.

Sigma 18-50 f2.8 (non OS) - absolute piece of sh*t. Worst lens I ever bought. Terrible below F4 and it is not really 18-50...more like 20-45!

50 1.8 - must-have for portraits when travelling. The old non-AFS version I had was fantastic for colour/contrast.

50 1.4 AFS - Nice lens but lacks the personality and "pop" of my old 50 1.8.

Sigma 10-24 - love this lens for travel. You get that huge wide-angle sky with lots of contrast.