Fast Intentions has one of the best build quality regarding manufacture of exhaust components, and their fit and finish is reflected in their pricing. FI also does the "little things" like smooth-out internal welds to make sure air flow through the pipe is as non-turbulent as possible. They also use thicker mating flanges and higher-quality SS, which matters especially for those Qs operating in salty, winter roads.
I have their Catted DPs and CBE installed on my '17 Q60 Red Sport for about two years, operating in Western WA state (no salt), and aside from the normal chrome burnishing that occurs from operation at temperature, the piping, resonators and mufflers are holding up well. And sound good, too!
The two questions you ask “best performing” and ”best tone” land you in different places. Performance will be similar for any of the lower down pipes in the 60mm to 2.5 inch size. The 3 inch pipes obviously flow more air but you don’t need and can’t take advantage of that large of pipe below 550ish hp.
Tone is a different question. All of the down pipes are going to increase the violent sounds of combustion. Some people like that sound. The pipes with resonators built-in will moderate the violent sound a bit for those with more refined taste. It is not a huge difference but every little bit counts if you are in that camp.
As was mentioned, once you decide on what size and type you want to run, price and quality are your decision variables. There is not a vast difference between them all in terms of quality. However, some brands are consistently better at things like weld quality, flange thickness etc. If name brand matters to you then price is what you shop.
You didn’t ask but I purchased HKS. Why? I‘m on the proceed quietly but quickly team. When I purchased my LDP’s, HKS was best priced resonated version.