When choosing a snorkel, like with any piece of equipment, you need to establish what you will mostly be using it for: snorkeling, freediving, or diving.
Snorkels that are used for the sole purpose of snorkeling, normally feature a fixed lower section that stays in your mouth comfortably throughout a snorkel session, like the Atomic Aquatics SV1 Contour Snorkel. The Tusa Reef Tourer snorkel features a cross-cut barrel design for easy clearing and is perfect for freediving. The Scubapro Spectra Dry Snorkel features a dry top to keep out any water and has a flexible corrugated joint, which makes this the optimal snorkel for diving.
Best of all, most snorkels are available in many different colours, so you can match them to your mask or your whole dive equipment setup.