The Smokin-it and the SmokinTex are very similar. In comparing the #3 and the 1400, the Smokin-it has a 1200 watt element versus the 700 watt element of the 1400. You also get a 12 foot cord with the #3, negating the need for an extension cord in most, but not all, cases. I believe the #3 casters are larger for easier rolling. And it is about $100. less expensive.
Both companies offer specials. Both smokers are analog, not digital. In the sites FAQ, you will read about the temperature fluctuations. NOT a problem.
Check the dimensions of the racks.
The #3 has two door latches and the 1400 is a single. Since these units do not employ gaskets, the seal is achieved through compression. It makes sense to distribute compression evenly so 2 latches appear to be better than one.
Check the FAQ on both sites. Also check the warranties very carefully.
Go to their respective forums and read the comments from the users. There you can read about problems and fixes, recipes, etc. Join both and ask questions regarding their experiences and why they chose the brand and model they currently use. If you join, feel free to PM some of the more active users.
Both smokers are manufactured in China and are of high quality and operate the same. The both peak out at 250 degrees, with most folks smoking at 225 degrees for ribs, butts, etc.
In the end, you will have to decide which is right for you. Just keep in mind that nothing is perfect, and once in a while a bad unit or a unit with a bad component ships. Both companies will take care of you.
The Cookshack is in a league of its own, being digital and very expensive. It is good.The temperature lock on and stays steady within a degree or two. BUT, you can get either of the smokers you are looking at, and add an Auber unit for about $200 and have the digital accuracy that many people want for far less than a Cookshack of similar size. TheCookshack units are made in the USA. And they do have refurb units on occasion at a reduced price.
Good luck.