It maintains parallelism, clarity, and proper usage in comparing the quality of blown glass pieces from Italy and Western Europe to those from the eastern Mediterranean. The correct choice is (E)
"The quality of early pieces of blown glass excavated in Italy and Western Europe far surpasses that of pieces from the eastern Mediterranean, not only with regard to the variety of shapes represented but also in terms of decorative techniques and functionality."
This choice maintains parallelism, clarity, and correct usage. It correctly employs "surpasses" to agree with the singular noun "quality," and the placement of "not only" is appropriate for presenting parallel elements in the comparison. Additionally, the use of "with regard to" is more idiomatic than "regarding" in this context. Overall, option (E) provides a grammatically sound and clear expression of the intended meaning.