I think #3 is the best of the set but its missing a little fill in light. This doesn't necessarily mean flash. You can use a reflector to push the light back on the subjects face. The umbrella and background are perfectly lit, but her face doesn't pop from the background. If you have an off camera flash, then a simple fill in flash with a softbox or umbrella would work.
I think 2 and 4 are the best.
Nice job on the exposure. Usually on a shot like 4 the highlights in the hair are inevitably blown.
I also think those two present the strongest image.
Just my .02 cents.