There is only a few dollars difference in price and a few minutes difference in arrival times between Nozomi and Hikari. The Hikari travels just as fast as Nozomi. The time difference is because it stops at more stations along the way. Unless there is just no choice, there is really no reason for tourists to use Kodama, which is effectively a shinkansen commuter train that stops at every little station.

As mentioned above, the slight extra cost of Nozomi versus Hikari is often offset by the frequency of departures - 10x per hour versus 2x.