The Upper East Side has always been synonymous with wealth,
while the Upper West Side has always been considered more bohemian
and intellectual, probably due to its close proximity to Columbia
University.
In the last 25 years, however, the Upper West Side has gotten
progressively more and more gentrified, and now rent and condo
prices on the Upper West Side are quite often even more expensive
than on the Upper East Side. However, the Upper East Side is still
generally considered the wealthiest neighborhood in the city.