I'll point out that you really have no choice about whether to have brakes or not. Most states require them on any towed vehicle weighing over 3,000 or 3,500 lbs, both of which you are going to exceed, counting car and tow dolly.
In any case, most folks will probably recommend electric brakes because they are much more adjustable in use. You want them to brake fairly hard when needed, but how hard they can brake depends on the surface. Dry pavement grips much better than wet, or gravel, so it's helpful to be able to change the braking force of the trailer/dolly depending on the load and surface. That is hard to do with surge brakes.