By default, you should use a vector. It has the simplest internal data structure and provides random access. Thus, data access is convenient and flexible, and the data processing is often fast enough.
If you insert and/or remove elements often at the beginning and the end of a sequence, you should use a deque. You should also use a deque if it is important that the amount of internal memory used by the container shrinks when elements are removed. Also, because a vector usually uses one block of memory for its elements, a deque might be able to contain more elements because it uses several blocks.