I really don't think it matters. Just springless steering arms and keep it greased. Everything else around it will fail before that bushing does and you'll most likely be changing it when you fix whatever break. I had the plastic ones and beat the hell out of it for a couple years and it had no wear on it at all. Damn knuckle broke first.
I've broken stock knuckles and bent the **** outta solid highsteer arms. Same stock type bushings through it all. I've put them back together with some dirt on them in the woods more than once.