Kettles are an excellent option for cooks that want a host and fast cook. Perfect for searing, grilling and hot and fast smoking. They are not as effective for low and slow cooks.
Offset Smokers can be harder to master but are recognised as the most authentic form of BBQing. You can safely add fuel without disrupting the temperature in the cooking chamber. Offsets also have significant cooking space allowing for large cuts of meat.
Vertical and Bullet Smokers also allows for significant meat cuts and can be easier to maintain than an offset. They are smaller in overall size than an offset to be stored easily. Adding fuel to a vertical smoker can be difficult. They can't be used as a grill as effectively as an offset or kettle.