I am a huge Weber fan, have been all of my life. I own several Weber grills, including a 18.5 kettle my dad gave me in the 70's when he upgraded to a larger kettle. I still use it at our cabin.
Since I got my Akorn a year and a half ago I haven't touched my other grills. Mainly it's used for my wife and I or small (6-20 people) get togethers. As others have said, it works great for different styles of grilling plus low & slow. I haven't made any mods to mine and have no problems holding 225-250 temps. I think as you use them they "gunk up" and seal themselves.
Also, because of it's design I feel comfortable using it on my wooden deck without fear of an ember starting a fire. I would not use my Webers on a wooden deck.
One thing that doesn't get much mention is that the WSM is very susceptible to wind & somewhat less to cold. We are in a pretty wide open area of Minnesota and I had to build a wind screen to protect the WSM to help keep temps steady. The WSM will eat up a fair amount of charcoal on a cold winter cook. The design and insulation of the Akorn makes it pretty bullet proof when it comes to wind and cold.
If you are going to smoke a lot of meat at a time for groups or a comp, a WSM and a kettle (look for a Performer on CL) might be the way to go. Or you could start with the Akorn and expand from there as you see where you want to go.
If I had to choose between the two right now, it would be the Akorn without question. But I'm gad I don't have to.
WSM, Green stainless Performer, Genesis 3000, 2 18.5" Weber kettles,