The Opening
The opening is the first impression a perfume gives right after you spray it. This is usually where the brighter and more volatile notes are noticed first, so citrus, fresh, aromatic or spicy notes can feel more obvious at the beginning. The opening is often the most attention-grabbing part of a fragrance, but it can also be the most temporary one.
The Dry-down
The dry-down is what the perfume becomes after the opening starts to fade and the fragrance settles on your skin. This is where the heart and especially the base notes become more noticeable. The scent usually feels smoother, warmer and more blended at this stage, and this is often the part that stays with you for the longest time.
Which One Tells You More
The opening and the dry-down can sometimes smell very different from each other. A perfume may open very fresh, sharp or bright and later turn much sweeter, woodier or darker. This is why judging a perfume only from the first few minutes can be misleading. In my opinion, the dry-down tells you much more about what the perfume is really like, because this is the version of the fragrance you will actually wear for most of the day.