A lot of factors go into the mask you choose. Your mask will affect your field of vision, your ability to shield yourself from outside light, the ease with which you can clear your mask, and more.
Dual lens masks stay close to the eyes, giving you greater peripheral vision. And since the lenses take up less space, they’re easier to fit with prescription lenses and easier to clear.
Single lens masks give you a broad, uninterrupted view of the marine scenery, since there’s no bridge blocking the middle of your field of vision. A single lens mask can also make it easy to maintain binocular vision.
Tri lens masks have a large single lens and a side window on each side of the mask. This gives the mask an open, airy feel, while giving you a lot of peripheral vision.
SCUBAPRO’s Full-Face Mask is a professional-quality mask used by military and commercial divers all around the world. The added comfort and safety of a full face mask is useful in all sorts of advanced diving situations. Full-face coverage is useful in cold water, wrecks, caves, and technical dives. It’s also useful on any dive that uses a secondary air source, or when diving in contaminated water.
If you're just starting out, you may be interested in sets that combine masks with other basic gear like snorkels or fins. And if you want to put your own spin on it, some masks can be adjusted for fit, comfort, and color with accessories.