For the record every cooker/smoker is a convection oven. Electric smokers use a fan and burning pellets or wood. Pellets use a fan to move air and burning pellets to create heat and smoke. A kettle or other uses coals to create heat (also smoke), wood to create smoke, and natural air current to move air. A side box burner or reverse flow same.
It all comes down to the smoke flavor profile you desire....
Charcoal based smokers tend to have a strong smoke flavor because a snake or minion method is often used and the coal start up process creates a stronger smoke, similar the wood burns slower creating a "stronger" smoke. My wife won't eat anything that is charcoal based unless the charcoal is 100% engaged before it interacts with food.....she said it tastes like acid to her.
A RF or Side box "can" burn cleaner because of the design and they tend to give a "smoother" smoke profile if they are burning well and have the right air/burn mix ratio. A properly burning wood burner will give a sweet velvety smoky overtone. My wife LOVEs this flavor but some times it can be a bit to much. WHEN I have time natural fire cooking is my favorite way and flavor.
A pellet smoker by design burns cleaner because it needs combustion for heat. The higher the temp the cleaner the smoke.....usually above 285 ish they have very little smoke The swinging temps on the old pellets would create more smoke because of the start stop combustion in the burner pot. Most folks that want a stronger smoke flavor use an additional pellet burner for smoke. The benefit to a pellet is simplistic of function. ANYONE can use one and get a very good flavor out of it. It IS nothing more than an "electric based" oven.
All this said, all 3 are different smoke profiles and one needs to choose the desired application for their situation. I have versions of them all and use them all based on the available time and desired flavor profile. For example, I am currently working and and can't watch/tend the smoker (the weather is also NASTY), but I have beef ribs on the RT 1250 pellet that will be ready for dinner..... So for me the Pellet is very valuable cooking tool and if I could have only one smoker I would have a pellet because it allows me to have BBQ many times a week all year long (I did spares last week at -1 deg and 35 mph wind) vs only a couple times a month with the wood burner.....