I have an 18.5 WSM, a mini WSM, and several kettles. I use them all for smoking. The WSM has a clear advantage when I want to do a lot of stuff and/or cook a long time. It is the only thing I use for pork butts because when I do them I do at least two and most times four at a time because it takes virtually the same amount of time and effort. The WSM takes the most effort and time to clean afterwards so that is also a consideration. I have really fallen in love with the mini WSM but it is a specialized tool for me. I use it for relatively short cooks less than six hours. For example, it works great for two slabs of BB ribs each cut in half. It is also perfect for pork loins and pork tenderloins. It is my go to option for fatties and moinks. I like to use 22.5 inch kettles, my Performer in particular, for single slabs of ribs. I prefer to do low and slow using firebricks. I also like to use the kettles for first time cooks because it provides easy access to the product and seems to not be as sensitive to opening and closing the lid as the others. It is also the easiest to set up and clean. When it comes to direct or indirect high heat grilling, the kettle is made to do that. You can do it with a WSM, but it is far from ideal.
Bottom line is when comparing a WSM to a kettle you are not comparing a Ford to a Chevy…you are comparing a pickup truck to a family sedan. There is lots of overlap, but they are made to basically do different things.
WSM, 99 & 09 Performers, 2-OTG, SJG mini WSM, Summit 420, Q100, Akorn, and Schwenkgrill