For any suit that I would recommend wearing, there are only three appropriate collars: notched, peaked & shawl. Each lapel has its place on a jacket, each lapel works with the suit, the occasion and your body to provide the proper or improper look.
Notched Lapels - these are the classic lapel on most suits. They are the most common and basic lapel on a suit. The lapel works great for any body type and compliments men of all shapes and sizes. Notched lapels look great on single breasted two button and three button suits. Keep in mind the width of the lapel, too wide the lapel and you will look like a gangster, too skinny the lapel and you will look like a hipster trying to be cool. Stick to a medium to narrow lapel, a width that is classic and timeless.
Peaked Lapels - this lapel is most commonly found on double breasted suits. When buying a double breasted suit, do not purchase it unless it has a peaked lapel. A notched lapel should never grace a double breasted suit. Peaked lapels can work on single breasted suits and formal wear as well. A peaked lapel on a single breasted suit is more formal than a notched lapel, because it has the same lines as a tuxedo. A peaked lapel adds width to the shoulders, so it should be worn on slighter men and men who want to accentuate the shoulders. Men with more girth and size should be cautious employing the peaked lapel.
Shawl Collar Lapels - typically is only used on formal wear. It is always used on one, two or three button tuxedos. I prefer it with a one or two button tux and really recommend sticking with the one button look. Shawl collars are also seen in sweaters, but rarely seen in non-formal suit.
Know your lapels and avoid faux pas like notched lapels on a double breasted suit.