I've been perfecting my pasta all'Amatriciana as part of the worldwide Virtual Sagra to honor and raise money for the Italian earthquake victims.
With such a simple recipe, the quality of the ingredients is so important as there's no where to hide any flaws. So far I've tried three different types of Italian pecorino, made with sheep's milk.
Most recipes in English call for Pecorino Romano. This is the longest aged of the three with more gamey sheep-ish intensity and saltiness in a flaky, crystalized paste. I've found it too strong and salty for the dish and have been limiting it to a small amount grated on top of the finished pasta assembly to add some random points of salt and umami.
New to me is Pecorino Crotonese from the Calabria region. Mid-way in age of the three, this has a waxy paste and middle range sheep intensity and salinity. It looks like Manchego with the brown wax and impressions of the mold, and tastes very similar with some nutty notes. It melts quite well. I've tried it as the sole cheese on the pasta dish, and it works well if you want to use just one.
If you can find it, I highly recommend Pecorino Toscano Fresco for making Amatriciana. It's the most similar to the fresher, younger pecorino used in Amatrice where the dish originated. Aged 30 days or less, it has the creaminess and smooth texture of youth and a mild salting. I've used it to toss the finished pasta, finding that its sweetness rounds out the acidity of the tomato sauce and adds a lovely creamy texture.
So, my winning formula is blending the toscano with the hot pasta, then grating a small amount of romano over the top to finish.