WD MyCloud EX2 Ultra for me. 4TB RAID, built-in support for Time Machine, iTunes, does all the usual stuff like media server and supports the installation of server side apps like WordPress. Cost me around £350. I also pay £7/month for 2 TB of iCloud space for off-site storage. TBH I don't use anything like its full capabilities, it just runs as a Time Machine backup for the laptops.
