Let's toss in another point of discussion.
Size.
Does one typically use a smaller softbox than they would an umbrella for the same shot? For example, I have 45" umbrellas. I use them for portraits (headshots all the way up to full length shots). Would I want a similarly sized softbox or could I go smaller?
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I honestly never really liked umbrellas, so I didn't play with them a whole lot and I am the furthest thing from an authority about them.
I will say that I use that 32" square softbox I linked for headshots all the way to 1/2 length portraits. Obviously a softbox has different sort of falloff (especially once you start playing with the distance from light to subject) and the spill is much more controlled than an umbrella.
If I want to do a full length I'll typically pull out a couple strip softboxes... like this:
Amazon.com : RoundFlash Strip Light Softbox For Speedlights and Most Flash Units : Camera & Photo
These are the ones I use on site for a lot of different things, but if I want full body shots in a vertical orientation these are my go-to. They pack down to practically nothing and are super fast to pull out and set up (and they can be hung from just about anything including each other, since I do a lot of more intimate types of shoots the spaces are often indoors with questionable access to natural light, in smaller rooms where not that many light stands might fit, and the light from the speedlights needs to be controlled with an iron fist) The light from these tends to be a little weaker at the top than the bottom, for obvious reasons, and they are only 35" long so the upper area of the body still typically gets it's own speedlight and modifier (if full length). These make pretty good rim lights too. It's not an ideal solution, but it is a very workable solution for the way I shoot and allows me to control the exposure/gel independently for each angle.
If I think I need a full length horizontal shot (laying down etc) I'll unpack one more like this:
Amazon.com : Valufoto 12"x60" Strip Light Softbox with Grid and Bowens Speedring for Nikon, Canon SpeedLight and Studio Strobe : Camera & Photo
I can't vouch in any way for the quality of this one, I don't own it, but it is very similar to mine. The greater flexibility in positioning/angling makes this one a decent hair/shoulder/accent/detail light in a pinch... at the cost of being unweildy, slow to set up and take down, etc.
Edited to add: The reason I use strip lights is because I often feel like I need to both control the light from my speedlights, but also to be miserly with it because they have such low power output compared to studio strobes. A large square softbox has a pretty big face that produces a really nice draping of light but it also puts out a pretty big swath of light which is just fine in many situations, but I like being able to be very surgical when it matters and apply light exactly where I want it and nowhere else.
I also really dislike the catchlights in the eyes from strip softboxes, I feel like it gives the eyes a certain sort of inhuman/serpentine look to it (which works out in many fantasy/cosplay shoots) but doesn't look as good when I am going for pretty much anything else.