A garment that is more an accessory, the waistcoat is available in different cuts. The western one is styled for trousers and suits. The eastern iteration works better with shalwar kameez, making for a good layer in case of formal functions. The fabric and patterns are endless, which you choose is about where you plan on wearing the waistcoat, with what other clothes and most importantly your budget.
A sleeveless upper-body garment, the waistcoat can be worn instead of or under a coat as well. The western cut is also worn under a suit jacket, as part of the 'three-piece' suit.
The eastern waistcoat, possibly originating to some Persian cultural influence spreading into the Subcontinent. There is a local iteration that is often worn on top of shalwar kameez, to add a hint of formality to the attire. Often at weddings or official functions, one sees men with a waistcoat on top of their crisp starched shalwar kameez. The local version has a band collar without and lapels and the fall at the waistline is straight all around. Very rarely do they have the V neck, styles from a past time may still have that neck. The two side pockets are generally closed and the chest-pocket is used for handkerchiefs to adorn one's breast. Available in many slight variations of design, as every tailor or designer adds a little something that they feel would make it more an original piece. As for colour and cloth, the variations are endless, there are winter waistcoats made from wool and summer ones made from cotton or mixed material. With some that are plain sober colours to funky ones with paisleys and all means of patterns on them.
The western waistcoat is more a style statement as a response to the French styles in the time of King Charles II of England. The modern western iteration of the waistcoat has quite a few varied designs, perhaps more than the eastern counterpart. The general look has a deep V neck collar so the shirt and tie are visible. It can be a straight line V, have angular lapels or have rounded lapels. The waistline in front has 2 'V' like points pointing downwards, a lot wider than the actual shape of a V. The number of buttons can vary from 3 anywhere to 5 or more. Often when a waistcoat is purchased as part of a three-piece suit it is the same fabric as the rest of the suit, but at times it could be a contrasting colour as well. Pinstriped fabrics are common in western waistcoats.
As a general rule, the last button of the western waistcoat is never closed. Available under many different brand names and a range of price points; which one you choose to purchase depends on the budget, fabric, cut and brand you like.