As my moniker implies, I do a lot of smoking/barbecuing and recommend a kamado style grill and smoker for backyard use. I have used a series of them over the last 28 years and find they are the most efficient when it comes to charcoal usage and heat retention. For those not familiar with kamados, they are made from high temperature clay and the most common brands are Big Green Egg, Kamado Joe and Primo. I have smoked at 275 degrees for 28 hours on 8 lb. of lump charcoal on my Primo Oval XL.
They are not inexpensive, but deliver great tasting food with minimal monitoring and maintenance.