Not suprisingly, the top two bay NAS listed is the Synology DiskStation DS712+. The DS712+ is the top of the line two bay Synology NAS with a speedy Intel Atom D425 1.8GHz CPU on board as well as 1GB of DDR3 RAM.
PCWorld summarizes the software that comes with the DS712+ (DSM4.0) as follows:
Like other Synology NAS boxes, the DiskStation DS712+, runs the company's Linux-based DiskStation Manager 4.0 operating system. This comprehensive software includes features like remote access via HTTP, HTTPS, FTP, SFTP, Webdav, and audio, video, and image servers. Plus, it provides iTunes and DLNA-certified media serving; a Wi-Fi connection via a dongle; and (new to the DiskStation Manager 4.0 operating system) the ability to serve as a Wi-Fi hotspot. The box also supports remote synchronization via Rsync or proprietary means; video surveillance; and more.
The DiskStation DS712+ is superfast and potentially vast (with the DX510 five-bay expansion unit), and it has a wonderful operating system.
Here is a video showing unboxing of the DS712+ NAS:
Having owned three Synology NAS models with similar specs as well as two of the DX510 expansion units, I can vouch for the speed and stability of the Synology models.