Very tricky question...
As near as I know, no one who might have a Stampede is talking about them yet... Based on the specs and photos, I think it's a interesting looking option... may very well become Rec Tec's biggest seller. It's extensive uses of stainless inside and out is a good thing... It's octagon shape is intriguing. The new controller on the Rec Tec grills adds some nice features such as dual food probes and WiFi, I personally really like the WiFi option, and of course having a food probe or two is also nice.
Silverbac ... Seems to have a pretty good following, for the short amount of time they've been selling these. I think it's biggest selling point is that it's a modestly priced grill that is made with some fairly stout components... No WiFi, no food probes... it's basically a sort of old school pellet grill that's built reasonably well and sold at a moderate/fair price. It's still got the basic 20" barrel design, which I personally find somewhat limiting in terms of efficiently using the interior space. Other then possibly protecting the bottom of the barrel , I don't think the 'double' wall at the bottom really does much for efficiency or anything related to how it will actually cook food.
Woodwind... well, it's main selling point I think is the ability to empty ash from the firepot without taking the grill's internal components out ( cooking grates, drip tray, and heat shield ). I'm not one to put a whole lot of 'value' in it's optional sear box... if I wanted to cook with propane, I'd have a propane grill around too, but then someone with limited space in their outdoor area might find that sear box very handy to have.
None have any 'direct grill' option that utilizes the wood pellet fire... unless you consider 'grill grates' as a solution to that, but grill grates can be used on anything, if you do see those as a solution. Rec Tec is the only one that has a PID controller... Don't hear too many complaints about the ability to control temps with the other grills, so PID itself might not be a deal breaker...
Personally.... I like convenience of WiFi and the probes with the Rec Tec... and it's octagon shape may prove to yield a tiny bit more extra space inside... so for me, the Stampede gets a slight edge over the other two... but that's just me. I'm sure I could cook fine food on any of these three ( or just about any other pellet grill ).
Ultimately it's up to you to figure out which features are most important to you.