Ok so you are looking to jump into the pellet grill world. Good for you! You have a big list of candidates so your decision will be more difficult. First a few things about pellet grills in general and some considerations...
Cost of pellets- you might save money on a cheaper unit but will you pay more later for more pellet usage? Do you have a local source for pellets at a good price? If so than this might not be a big issue. The more a pellet grill eats pellets the more it can cost you $$$
Pellet grills for smoking- Pellets are wood and do produce smoke. Some pellet grills can produce more smoke than others. But they will not produce the flavor of smoke that you get from a stick burner. Pellet grills work by causing wood pellets to combust with the inducement of air. And by doing so there is less smoke. The absence of a flame will produce the best smoke but a flame out on a pellet grill is not a good thing. Some pellet grills like my Memphis will bellow the fan on and off to help create smoke and keep tight temperatures. This works pretty well however if you like heavy smoke flavor than a pellet grill might not provide that level you need. I personally like the lighter smoke flavor that a pellet grill produces. You can add a smoke tube that you fill with pellets and light to create extra smoke flavor to any pellet grill also.
Heavy gauge versus insulated- heavy gauge steel has it's benefits for durability but heat loss can be a problem. Heavy gauge steel can take a while to heat up causing you pellet grill to take longer to reach proper temperature. Then the energy that it has absorbed can be easily whisked away by a cold breeze. The more air movement over the metal the more heat loss. Insulated however has a thermal barrier between the inerior metal and the outside air. This barrier can be double wall(air) or actual thermal insulation(fiberglass). The outside of the unit remains cool due to this barrier and therefore heat loss is greatly reduced. Also insulated pellet grills tend to have a much higher temperature range for grilling due to being able to sustain those higher temperatures. One downside to insulated grills is that during the summer when temperatures are really hot you might find it difficult to sustain lower temperatures.
Steel versus stainless- Steel can rust. Powder coating can peel. Good stainless steel has much less of a chance to rust and will not peel. It can be a real bear to keep looking shiny however
Controller- The brains of the operation. A good controller will keep solid temps and reliably keep the fire going. Some offer remotes, Wi-Fi connectivity, built-in meat probes etc. As far as controllers MAK excels in the cool factor with it's pellet boss.
Weight- Does the grill weigh as much as a mini-cooper? What if you got to move it around? Sure it's got wheels but so does a car! You push your car around! You want something light and nimble? Or is your pellet grill going to stay stationary and not be moved? Something to consider.
Ok so you mentioned the Memphis Select as one of your choices. I happen to own a 2011 Memphis Select pellet smoker. I am very happy with mine. The only thing I would have done different at the time is stepped up to the advantage.
The Memphis is quality built. The thing is entirely made of stainless! The only things that are not stainless are the electrical components and the wheels. Everything else is quality stainless. Even the unique firepot is stainless!
The pellet hopper(12 LB) is located at the front for easy loading. Why such a small hopper you ask? Well when you average 0.50 lbs consumption an hour of pellets at 225F you don't need a large hopper for overnight cooks
The firepot is located at the center of the grill. Makes sense for more even distribution of heat IMHO. Also the pellets are fed up the short throw auger and slide down a chute into the firepot. Unlike other designs the chance for auger tube fire or hopper fire are almost impossible. And the hot rod(igniter) is located just under the firepot and not in the firepot like most other designs. The reduces fatigue on the igniter and allows Memphis to use a hot surface igniter like you find in a oven. Less exposure to direct heat and ash will improve performance and life of the igniter.
The hood is double wall and cool to the touch when in normal operation. When the grill is set to 550F the hood gets really warm but will not immediately burn you if you touch it. That is the insulation doing it's job.
The Memphis keeps very accurate temperatures across the board. Anything from 180F to 299F runs in smoke mode. During this mode the fan turns on and off to bellow the firepot and create smoke while maintaining very even temps. The 300F and above changes it to grill mode where the fan runs at high speed to maintain those higher temps.
The controller has a bright and easy to read display. It also uses an optional meat probe that can be programmed not only to display the meat temp but also turn the temperature down once the meat has reach it's target temp. The controller is also very user friendly and works almost the same as your home oven so practically anyone in the family can use it. It may or may not be a good thing
And all that stainless is just gorgeous! It is quite a beautiful grill. Sleek and stylish. Looks great on any patio. When cleaned with a quality stainless steel cleaner my grill looks almost as good as the day I bought it.
Comes with thick stainless steel grates and thick stainless steel drip pan. Also the hood is domed for higher profile meats and has a large capacity with the option second shelf grates.
And the grease tray is located inside the cooker instead of outside where the dogs can try and get at it or it spill onto your nice patio deck. The tray slides out and uses removable aluminum tray inserts for easy clean up. Then slide it right back in. It is located down in the pit away from the firepot and works great!
I think that covers it. If you have any other questions let me know. Good luck on your decision!
