Solid versus PEM is like diesel versus gasoline. You will never see a gasoline engine in a class 8 truck just like you will never see solid in an intermittent power application. While both could work, it makes no business sense.
Stew, plenty of room for all of them to succeed and be profitable. Of the hydrogen companies you listed in your post, I am invested in PLUG and FCEL, PLUG has the most comprehensive offering, FCEL for its carbon capture technology.