I've got a water or bullet smoker as they're sometimes called.
You can cook some excellent barbecue in them. I would recommend getting the charcoal type and then buy the electric conversion so you can use them a number of ways.
They are limited. You can't cook large foods in them. The lowershelf doesn't get as smokey and you have to work ribs vertically which is a pain.
These sorts of smokers do transport fairly well though.
I've seen some propane powered square towers lately. I like their arrangement and shelf capacity, but I'm not excited about using gas for barbecue. I'm not sure they'll hold a whole slab of spareribs intact and laying flat either.
I'd like to get a real fire based one with controllable draft. A 50 gallon drum size plus firebox would be right for me. Hold four slabs of ribs nice and flat, or a whole BIG turkey, a whole rib roast. Room for plenty of smokey sides as well. Haven't found one designed like I really want yet.
www.smokering.net has plenty of interesting information. Browsing through that is a good idea.
Phil