The best bag is always the "next" bag.
Do you have to worry about theft from the vehicle? If so, I'd lean toward a less photo-obvious bag.
When you say "work from the back of a SUV", do you mean within a few feet of the vehicle? If so, then a flip open case (such as the Halliburton might be easiest. But not if you're carrying any distance.
In any case, you may want to use a belt pack or fanny pack for the odd bits so they're handy.