Hi Jeff
Ive never tried Suncart im afraid, but for what you get with CS Cart, I have no reason to conisider anything but…
Most mods on the forum are built by users of the software and shared freely
they are usually accompanied by step by step integration guides, best thing is, if you have difficulties, theres more than enough of us on here to help you through it !
I used to use SunShop and would strongly advise against it. The cart has nowhere near as many features as CS, is much harder to template and mod and had lots of errors. Their support was very slow, if they replied at all, and when they did they just usually said something like “the cart doesn’t do that” which was no help to anyone.
It is much easier to work with CS and their team, and there are people on these forums who actually have a clue. I think SS cashed in on novice users a bit, the forum was just full of questions and never any answers.
My current site was sunshop before I moved to CS. Due to the nature of my site I need lots of mods done to the code. I submitted for a custom development quote from TWT early 2004 and have yet to hear back! I contacted them several times regarding it and they just said that they would get to it when they could! With CS quotes normally take 24 hours or less and are reasonably priced - plus I’m more than happy with their work.
I must add that they were working on a major new version when I left, last time I looked it was still in the making, so it may have improved… But I personally would still steer well clear just based on their support.
If I can transfer it you are welcome to my old license - its ‘expried’ but that just means you cant upgrade or get ‘support’ (as they call it) and I guess you’d have to run whatever version I was on. But honestly, don’t bother!
Simon
We took a pretty long look at SunShop ourselves. They do have a few nice features that we would like to see in CS (including the ability to designate that a specific product is not combined with others when it ships).
In the end, we spoke with maybe a dozen users/former users of the cart who all basically said the same as Simon. I know for a fact that they did not take the time to answer our pre-sales questions. From my personal experience, if a company can’t be bothered to make the effort for a sale, they are not very likely to expend any more effort in a support situation.
Besides, CS-Cart rules! 
Bob