If Dr. Sisti recommends the retrosigmoid approach, then I would consider Dr. Post at Mount Sinai. He recently did my AN surgery. I chose him after seeing several doctors including Drs. Roland/Golfinos, Sisti and Slattery. It was a tough choice between Dr. Post and Drs. Roland/Golfinos, but I downloaded their academic papers and found that Dr. Post has been particularly innovative in the field of retrosigmoid surgeries and reports the best success rates for hearing preservation and lowest complication rates. (I was focused on tumors the size of mine, about 1.5cm, so you should do your research as well.)
Frankly I also didn't care for Dr. Sisti. He recommended radiation, which is fine; but while I was in his office, he discussed another patient's case on the phone in front of us, he left the door open, and he talked way more than he listened. I believe he's also less experienced than Dr. Post - he said he'd done 300 surgeries, and Dr. Post said he's done about 500.