I got the Netgear readynas 104.
It's great on most fronts but there are a few quirks.
Pros
It takes 4 bays
It can install plex in it
It can do link aggregation
It's really quiet, much more quieter than my Drobo, both unit has 1 fan.
It is really well built, it weight probably about 2kg when empty.
Con
Some reason when I turn on the inbuilt antivirus I can't transfer files.
Plex plays some movie, not others. Not sure which as they are all mkv, all difference res, file size. It can decode a 30G 1080p DTS then won't transcode something like 500mb 720p file. It's not a massive problem as for pure NAS use, the until is great value for £180.
I have 4 x 3TB WD reds in mine, running netgear's x-RAID, it's a bit like RAID5.
The netgear is not perfect but it is about £250 less than a 4 bay offering from Synology.