While I haven't heard of failed forends that are one peice/pinned, If you are asking my opinion, then the steel action slide tube assembly is much stronger.
Heres the deal. I bought a Mossberg 500 late 2012. It was a combo set-up from Cabellas. It came iwth a 18.5" home defense barrel and a 28" vent rib (w/ changable chokes) sporting barrel. It was a decent price so I went ahead and bought it. What I didn't know, and found out soon enough, was the Combo deal from Cabelas used a pinned forend (to keep the cost down with the added barrel.. no wonder such a good "deal").
The forend was a bit slippry for me and I wanted to change it to a Hogue rubber forend. That is when I found out about the difference between pinned and tube assembly. Cost me a boat load to change out the forend becuase I had to also buy the tube assembly as well as the new forend.
Removing the pinned forend, I got a good look at how cheap it really is. After I put on the Tube assembly with the new Hogue forend, it was like a different gun.. no more slop while pumping the action and much stronger overall.
If I could go back in time, I would tell myself to skip the Combo deal and buy a persuader with the tube assembly.. then buy another barrel later.
I just went and got my pinned forend I took off and took some pictures for you to look at. The forend is all plastic (with exception of the action bars) and the mechanisim that is supposed to make it tight is a thin piece of spring metal.. If you look, you can see how it could break. Compare this to the tube assembly I linked above and you make the call.
Like I siad, my opinion, I would never buy another shotgun with a pinned forend.