I've got a grill dome.
They are the most efficient use of charcoal money can buy, but it takes years of use to make up the difference in cost. It's also the easiest thing to keep at temperature for long periods of time. As it burns, it cools a bit. So, get the temp up around 250*, wait 8 or so hours and it should be around 225* with no work involved. Nudge the vent open a bit, and wait. It'll be 250* within 20 or 30 minutes.
The biggest problem is capacity. They are not big. One brisket and it's full. Course, mine is the medium size dome, some are bigger. I have yet to get a double decker rack, but it's supposed to double capacity. Get the biggest you can afford. I picked mine up on craigslist on a lucky break, so I got it cheap and couldn't be picky on size.
I personally have only smoked on mine once, and it went ok. I need more practice. However, it is awesome for a steak cook. You can pretty easily get up to around 800 degrees to sear, and I've been told 1200 is not unheard of. Check out www.nakedwhiz.com
for great info, mostly pertaining to the BGE, but they are all the same.
Roasting at 350* for 2 hours is also a breeze, so I typically have used mine for whole or spatchcocked chicken.