I haven't used Witch Plugin, but I can't imagine it's good for portraits. I mean, I don't know what it does, but presumably if it turns their skin tone green and puts warts on their nose then you're clients are going to be unhappy.
I'm sorry, I couldn't resist. It's Friday and all.
Just a quick note on plugins. Nobody will be able to tell you which ones are good. Have a look at portraits online, there is a very wide gamut of what people consider acceptable post processing. Some people seem to like completely obliterating any detail in the photo, thankfully most do not. But I'd guess some of these overly soft portraits are from cheap plugins, poorly used. Even some of the high end plugins are too much for some people, who argue that any time you automate touchup it hacks the details. It's a personal thing, nobody can tell you what's right. It's going to matter on what you like, what you're capable of (Photoshop skills versus a completely automated plugin), what your final format is (you can get away with a lot more when your final product is just a Facebook image), and what kind of time you have to put into this.
I prefer doing most of the work myself, though I do use Imagenomic's Portraiture on occasion when I need to speed up my workflow. It's not free, but it does do a pretty impressive job once you get things figured out. Even then, I use it relatively lightly, and then I mask the layer and only paint it in where I want it. If I'm not pressed for time I just prefer the results I get with Frequency Separation. If I'm doing something really high end I most do my touchup through micro dodge and burn - a very time intensive process. But that's me, and I don't crank out a lot of professional portraits. Those that do obviously won't spend that amount of time on it.
Sorry I can't recommend any free plugins, but I thought this might give you something to think about. I'm going to guess that most free plugins will be a case of - you get what you pay for. But it can't hurt to try.