I've used all but the Ute. I've also build custom unified Xtracycle frames. If you need to carry a lot of weight regularly, I'd go with the Mundo. It's designed to carry a lot. If not, it is a heavier frame and does not have the advantage of all the Xtracycle accessories.

On the Radish vs Surly, I'd tend to go with what you can afford and what kind of riding style you have. Yes, the unified frame is stronger, less flexy, but I don't find the difference there to be that major. In fact, if you have a decent mountain or commute bike that you like to ride already, I'd highly recommend upgrading it with a Free Radical kit instead as a very economical option.

The Radish is designed to keep you upright, good for general around town riding. The Surly is designed to customize, so if you want a more aggressive riding style or something different from the Radish, you have that option. I'd look more at riding position and style than anything else on these two.