Whether you want to play around in a lake or pool or dive amidst coral reefs, your snorkel will allow you to do so while breathing underwater. There are numerous options to consider when selecting a snorkel to meet your needs and ability level.
Enable you to surface swim and breathe when you just want to play in the water without fully submerging
When scuba diving, they allow you to conserve air in your tank when you surface
Size/Design
Snorkels with smooth, continuous lines rather than unwieldy turns in the path of airflow will enhance breathing
Larger diameter snorkels also make breathing easier but the downside is it's tougher to clear them of water
Longer or curved snorkels let in less water from splashing but create more dead air space
Snorkels with flexible tubing at the turn of the snorkel tube fit better and allow you to switch more easily from your regulator to your snorkel
Bigger snorkels often have more features, keep out water better, and may increase comfort and fit
The disadvantage usually runs from increased dead air space and greater difficulty in clearing any water
Dry comfort
The dryer the snorkel, the easier it is to breathe and lesser the need to clear it of water
Longer snorkels provide this built-in advantage. There are some other features available as well:
Dry airways are a modern, sophisticated version of the ping-pong ball, which provides a seal until air is expelled, to keep water out until you blow. However, these do add bulk.
Some manufacturers compromise by using splash guards or water deflectors, which are simpler and therefore less bulky and expensive
The drawback of these is that it is more difficult to clear the snorkel when it fills with water
Some models offer these as an add-on, which gives you the option to use them for your different types of diving
Reservoirs
Some models of snorkels come with reservoirs to trap the water you couldn't clear or minimal splash
These add to the bulk and work best when combined with purge valves, and one-way, non-return drains built-in to some snorkels
Purge valves are especially useful for surface swimming since they can drain any water above the waterline, making it far easier to clear any remaining water
Small baffles or plastic or silicone, internal deflectors are positioned near the reservoir and purge valve to make it easier to clear a snorkel and to keep them drier
Composition
Most snorkels are made with plastic and silicone to increase durability
Those that come in parts or sections offer the option of replacing a damaged piece vs. the whole snorkel
A removable mouthpiece is a nice option since it allows you to change to meet your needs or when it becomes worn
Attachments
Most snorkels offer adjustments that enable it to be attached to the mask securely
Those that slide, lock and swivel make the attachment and adjustment process far easier
