Hi,
"Best" depends very much on the objects physical traits, the distances you need to measure and the precision you want/need. There's no sensor that's all round best (well, perhaps a pro LASER scanner, but it's too expensive to be a serious contender in hobby robotics).
The Sharp distance sensors goes up to 5.5m.
(
Sharp Comparison Sheet)
This comparison of different rangers (IR and US) doesn't list the above mentioned Sharp sensor and US can be used at a larger range than what's mentioned, but it's informative none the less.
It doesn't mention LASER rangers either (Like used by eg. Bushnells) - rangers, not scanners - which is yet another way to shave that goat, but I think that you'd have to hack a device containing such a beast, as I haven't seen any sold as just the ranger unit alone.
A LASER ranger will obviously be the most precise and able to measure the distance to what's covered by the small LASER dot and at a much larger range - Tank LASERs work on at least up to a few miles (I should have gotten some when the Russian Army had their large "closing sale" way back - seriously high powered IR LASERS, around 40W IIRC - I could have gotten all the cats in the 'hood... In one shot
).
Electronic measuring tapes using a LASER are expensive but works A+.
In comparison, the US measuring tapes are just bareable on a good day, if you have a large bare wall in an empty room, don't need too high a precision (i.e. a bit better than eyeballing it) and don't breathe too heavy, but in a furnished room... Pure Monte Carlo (at least that goes for the units I own and others I have tried).
In summation: Select your sensor after your targets
size, shape and range.