The answer is all three! Not at the same time and they can’t be confused to be appropriate for every occasion but the great thing about a waistcoat is, unlike a cummerbund, they are they accessory that goes with all types of neckwear.
Great for either formal or casual attire, a skinny tie looks great with a waistcoat and is now fast becoming an option for weddings if you aren’t going for the traditional style big day. A waistcoat adds a simple something to an everyday business suit; this is obviously where you’d wear a standard necktie. I’m not sure how many offices accept cravats as every day wear. Traditionally, wearing a belt with a waistcoat is not the ‘done’ thing, they were supposed to cover the braces used to hold up trousers but it’s today’s styles it has become more acceptable to wear a belt with your waistcoat. Just make sure that it is of complimentary colours, for example a brown belt with a navy waistcoat
Popular with Dr Who and other time-lords alike, the bow tie is becoming rather fashionable again. Worn in a formal setting for black tie events with matching black bow ties and waistcoats is a dapper look for any modern gent. Or worn in a casual setting with a tweed waistcoat and primary coloured bow tie is no longer crazy granddad, more like Pinterest-worthy outfit. A bow tie needs to be worn with a waistcoat or cummerbund to avoid your bow tie appearing stranded at the top of your shirt.
Unlike the other two, a cravat can’t be so casual. Even if it’s worn in a non-formal setting, you will easily be the smartest guy in the room if you don a cravat. A cravat must also be worn with a waistcoat to avoid it looking lost at the top of a shirt, just like a bow tie. Perfect for weddings, cravats are the most stylish neckwear for these sorts of formal events.
A top tip when finding the perfect wedding waistcoats are to ensure that it fits well. There should not be inches of shirt visible below it, but there should be a small amount. Also, it is custom to leave the bottom button of a single-breasted waistcoat un-done. This comes from stories circulating King Edward VII, when it was said that he needed the bottom button un-done due to his expanding waistline. But, it is also useful for sitting down, as this actually strains the bottom button anyway.
DQT’s Wedding Waistcoats available here: http://www.dqt.co.uk/waistcoats.html