We get emails all the time asking about which style of diving mask is better, a single large front lens, or a two lens design. Our answer is...whatever you prefer! The most important thing is that the mask is comfortable and fits your face correctly. Dual lens masks can sometimes be lower volume which is nice if the glass sits closer to your eyes, but in general the difference is not usually too noticeable between one lens or two. One thing to note is, that if you require prescription glasses, it is much easier to find a prescription dive mask with 2 replaceable lenses, due to the fact that each eye can require a different level of lens correction.
Lens SIZE one the other hand can make a big difference. If your diving mask is too small, it can cause a claustrophobic feeling due to the silicone skirt and frame obscuring your peripheral vision. Panoramic style masks can help certainly help alleviate this problem, but in that case you might have a small seam in the corners where the side lenses join which can sometimes cause minor distortion. This isn't too big of a problem for most people, but some divers don't like this effect.