Like tltt above, I've never seen a quality assisted-opening stiletto, and I'm all about folding stilettos.
But if you're looking for a large, manual-opening, heavy-duty stiletto, one with a strong reliable lock, one that can be easily opened with just a flick of the wrist, then I would recommend the Cold Steel Ti-lite 6 with Zy-Ex handles. I own a few. The Ti-lite 6 is my all-time favorite stiletto, and also my all-time favorite knife.
I specifically recommend the Zy-Ex handle version over the aluminum or G10 handle versions because from my experience those models don't open nearly as easily. The aluminum handle version has a bead-blasted blade, and the bead-blasted surface causes greater friction in the pivot than the satin bladed Zy-Ex version. And the G10 handle version has a black coated blade, and the black coating creates increased friction as well.
Here is the Cold Steel video that convinced me to buy my first Ti-Lite 6 with Zy-Ex handles. In particular, I was impressed by the demonstration of Lynn Thompson repeatedly stabbing the steel table (starting around the 6:22 mark), without any failure of the knife. It didn't break, the lock didn't disengage, and the knife was still functional afterwards. Naturally no one is ever going to need to stab a steel table, but it demonstrates how strong the knife is. There's no way I believe any Italian stiletto, or ANY other stiletto for that matter, from any maker, could ever survive such abuse.