All of them.
Light from a small source will have the very crisp quality you usually see on TV shows: they use several fresnel spots. Grids are a photo equivalent, to some extent. Grids may prevent most lens flare problems, although adding barndoors is a good idea. And hairlight will be restricted to a smaller area, say enough for a twosome, with gradual fall-off.
Ordinary reflectors with the necessary barndoors will work fine too. A half-spun diffusing material may spread the light in a more uniform pattern.
Always check for spill light that may come from hairlights on the background: spill is easily blocked with blackwrap and clothespins added to the barndoors when necessary.
Softboxes make very nice, subtler hairlights. They definately have more "class" than the regular hairlights (in my view). Problem one is suspending over the subject. High ceiling required, maybe heavy duty boom required, if you can't suspend from a plaster or acoustic tile, etc ceiling. Second is lens flare: not practical in most cases to gobo-ize the softbox: much better to gobo-ize the camera, maybe using what's called a "french flag", or any other old flag, piece of foamcore. Third is adjusting this heavy apparatus.
In all cases, security first: any equipment that is suspended over people must be secured with steel cables, or even a good rope will do, but in a private studio, there are no excuses for not taking these precautions: a hot barndoor that falls onto someone's face could be catastrophic. On location, extra care is taken to prevent such accidents, not letting people bumping into stands, etc..
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Jean Bernier
All photographs are only more or less credible illusions