The following brief analysis might help you when choosing the most efficient representation for a concrete case. n is the number of (non-zero in sparse case) elements in the vector.

Performance comparison
Operation	Vector	SparseVector
sequential iteration	O(n)	O(n), but with greater overhead constant
random element access	O(1)	O(log(n))
append an element	O(n) + reallocation costs	O(1) if no preceding random access operations were performed on the sparse vector; O(log(n)) if there already were random access operations on the sparse vector