I have a few WSM'S and few drums (one is the big poppa kit). If I had to pick only one, it would be the WSM and here's why.
Let me start by saying that they both are equally as fuel efficient from my experience and they both put out amazing food. You really cant go wrong with either.
However, I do feel the WSM is slightly more versatile for the price. For starters, it is a water smoker. Some like that style of cooking and some don't. It produces a slightly different flavor profile than cooking on a drum. In saying that, you can get the EXACT same flavor profile on the WSM by simply taking out the water pan. I mean, it is essentially a barrel style cooker.
All accessories that you can buy for a drum can be used on a WSM. For example, gateway drums sell am awesome rib hanger that fits perfectly in my WSM. It's like it was made for it actually. If you've never hung your ribs, you have got to give it a try.
The shape of the lid on a WSM gives it a slight advantage over a traditionl drum with a flat lid. You can simply put more food on it because of the extra room under the lid.
I understand it is called an "ugly" drum smoker. I think a drum can be built to your taste, but the WSM comes porcelain coated. It wont ever rust if taken care of. If you are worried about longevity and appearance, Weber all day. They last forever and shine up like new years down the road. Not to mention a 10 year warranty on the porcelain? Weber's customer service can't be touched.
As I said, I have both and love them both. They are both fun to cook on but I do feel the WSM has its advantages. Probably the only real advantage the drum has is the price (if you build). You could build a drum easily for under $100. If you go the BPS route, your looking at around 140 just for the kit. Several hours of prep and putting together depending on how detailed you want to be. A new WSM will run $400. I bought mine used on craigslist for $100. I see them all the time in my area for around that price.
Hope this info is helpful. You'll be happy with either.
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