it depends on what work flow you want to use.
do you want to create your own forms? whith out the styling of CSS Form builder, but still have captcha or date picker?
Then use Form Toolkit.
Do you want to create forms that are styled using CSS Form builder? Then use CSS Form builder.
you can install both form builder and form toolkit at the same time to can access to the HTML Editor.
CSS Form Builder contains all of the functionality of the standalone extensions.