You have zeroed in on the all stainless steel models. I would look carefully at warranties, who has what and for how long such as 3 years, 2 years, etc. Also look at the standard features such as wheel size and cord length, number of door latches, heating element wattage, rack size, and the like. Check out each site for owner comments, pro and con. Look at their accessory list and parts list pricing.
Use the search bar at the top of this page for each brand of smoker you have mentioned. I think you will find that of the brands mentioned by you, the Smokin-it line is a lot of smoker for the money with a very strong following. Just keep in mind that these smokers are analog, not digital, and temperature swings of 20 or 30 degrees high and low of your set temperature are completely normal and explained in the frequently asked questions section of the manufacturers site. If you want digital accuracy to within a couple of degrees of your set cooking temperature, you can always add a digital controller. Another aspect to consider is capacity. You can always smoke less in a large smoker but cannot smoke more in a smaller smoker. Just something to consider.