How Do I Find A Good Mask For Snorkelling Or Scuba Diving?

All masks have a different fit so it is essential to get the best one for your face. It may not be the most expensive one that is right for you. Similarly buying a cheap one that doesn't quite fit will just cause your mask to flood continuously.
Mask can be rubber, plastic or silicone. Silicone is the longest lasting. A silicone mask rinsed after use in fresh water will last more than 15 years. Rubber is next best but will eventually perish. Plastic is only recommended as a last resort. It neither wears well or fits comfortably.
A mask must be fitted with a tempered glass window. Plastic just scratches and after a day or two on the beach will be foggy. There should be a skirt around the inside of the mask to ensure a good seal. There should be a nose pocket which can be squeezed to help clear the ears and finally a restraining strap.
Check the fit by placing on the face without the strap. Sniff in. The mask should stay on your face without any help.