Hey Phil,
I’ve had and used both in the past. Over time I abandoned the rubber in favour of the plastic or metal. I found the rubber ones tended to tear in places where they commonly folded. This was no big deal as they were inexpensive but a pain none-the-less. It is true the hard plastic hood can be a annoying to store. That being said they provide a bit more protection than collapsible rubber. You have a major investment in that DA *300 and if the hood offers any protection at all it seems prudent to use it. Furthermore the DA hood will be designed to provide optimal protection from stray light for this particular lens. Can the same be said of an after market rubber one? Vignetting might be a problem if it doesn't fit properly. My killer blow, if it can be called that, is the hard plastic hoods just look better. After all you have a killer lens in that DA *300 and you might as well enjoy the massive bragging rights that come with it.
Tom G