My top recommendation is still the Crucial P2 1TB 3D M.2 SSD, a drive that makes it to the top of the list because of its affordable price, excellent performance, and high reliability.
Gen 5 PCIe SSDs are here now too, so if NVMe speeds seemed ludicrous already, hold onto your hats. Annoyingly, the support for Gen 5 drives isn't quite here yet, and for the majority of users ...