Using STS-V circuits is definitely more efficient, especially when transporting non-SONET based services (like fast ethernet). It can also provide the flexibility in the future; as STS1s are readily more available than STS-3C or higher contiguously concatenated bandwidths; as well as in-service bandwidth upgrades (if supported by the terminating line card).
The only negative "might" be is if there is an inter-carrier hand-off. The carrier may have some additional charges due to the handling of multiple circuits.