If you are planning to do any snorkeling, choosing the right snorkeling mask is the most important thing that you will do.  I can tell you from experience, if you have the right mask, you will absolutely love snorkeling. On the other hand, if you buy a snorkel mask that is uncomfortable or doesn't fit properly, you will not enjoy your experience at all. That's why it's important that you take your time and choose the right mask! If your kids are snorkeling with you, the same is true for them - they will be much happier if they have a mask that fits well. 

The most important thing about a snorkeling mask is not the price. In some cases, better made masks will cost more than cheap ones, but that isn't always the case.  You can often find a very quality mask that is moderately priced.  

When you head to out to choose a mask, your best bet is to do to a dive shop, where they have employees who can assist you with choosing a mask. 

You'll first need to decide if you need a small, medium, or large mask.  Children's masks will have their own sizes.  Once you have a basic idea of the size that you need, take a mask that you like and place it on your face without putting the strap around your head. Suck air into your nose gently. The snorkeling mask should fit perfectly against your face without having the strap.  If it does not, using the strap won't help to keep water out, and your experience will be a nightmare.  Move on to another mask until you find one that fits your face well. 

Now, you'll need to make decisions on things like a purge valve, lens type, and color. 

The purge valve allows you to get rid of water in your mask by exhaling through your nose.  Masks that have these may be slightly more expensive, but do save a lot of time that you'd otherwise spend clearing your mask of water. 

Very cheap children's masks may be made with a plastic lens. Stay away from these for snorkeling purposes. You want a mask with tempered glass.  Look for one that is anti-fogging as well.  

The color of the lens is not that important, but for those who are new to snorkeling, light colored lenses may be best and will help you to feel less claustrophobic.

Pay attention to price as well! Don't break the bank for a snorkel mask that you are going to use for one vacation!