al sf bay
There are two (2) big differences: the controller is one, and the other is that the CS is made in America. Both add to the cost, and that is not a bad thing. But there are other differences which give the SI unit some advantages. The length of the power cord is one such advantage. Extension cords should be avoided whenever possible. A 12 foot cord gives some flexibility in smoker placement. Wheels: my 066 has small wheels that get a tad hung up on the patio negotiating paver bricks. The SI heating element is of a higher wattage. The SI 3 has larger racks, stainless steel. Mine are chrome, and stainless racks are (or were) an option. Accessories and parts are less expensive for the SI units than those for SmokinTex (ST) and Cookshack. Check the warranties carefully, and the return policy and time of return. I believe you eat the cost of return shipping no matter which company you go with.
Digital is nice. Is it necessary? No. Read the FAQ on the smoker sites. Analog will swing 20 to 30 degrees (or more) on the high and low side of the set temp, and this is normal and averages out over the during of the smoke. Digital keeps it tighter. But a 16 hour smoke is still a 16 hour smoke, regardless of the use of digital or analog. My brother has the SI 3. A remote thermometer like the Maverick works well for monitoring internal meat temperature. And he has not had a bad meal since he received the smoker. Nor has he experienced and problems with the smoker. If you want digital, you can add an Auber unit to a SI smoker at a later date for far less than a CS with built in digital. Either smoker will do you well, but I would look at the budget, read the posts on the SI and CS forums, as well as search here for SI posts.
One thing I have noticed over the years is the obsession for accuracy. Many owners of the SI units use them straight out of the box with good results. Some (many?) will drop a remote temp probe through the smoke exhaust hole in the top and freak out over the temperature swings. They expected digital accuracy. Well, the FAQ on the SI and the smokintex sites cover this very well. But it seems unacceptable to them. So read first. The only time I would worry about the temp would be on a long smoke of butts, brisket, or from a safety factor, poultry, and then the probe goes into the meat. The food is done when it is done, whether your smoker is analog or digital.
As I said earlier, you cannot go wrong with either unit. Were I to do it all over again, I would go with SI. At the time of my purchase a few years ago, and for the size I was looking for, I wanted a unit with 2 door latches and SI had only one latch. And the ST while it had 2 latches on the 1500, had 2 heating elements and that struck me as odd. The ST is every bit as expensive as the CS but is analog. Go figure.
I hope this helps.