I have a Seagate personal cloud NAS and it works well for now. I'm avoiding most transcoding issues by only using .MP4 files, and going with 720p instead of 1080p.
Some movies just will not play in the same format as others will and I don't have a good understanding yet of what the problem is.
I might be replacing my laptop soon and thought that I could use the i7 core to do any work I need which is almost certainly powerful enough to transcode anything I have. So if I ran Plex on my laptop instead of the app on the server, and only used the Seagate as an external HD to the laptop, like this:
TV <-(HDMI)-- Roku ... Wireless Router <-(cat5)-- laptop running Plex <-(HDMI)-- Seagate
... would that work better than running the Plex app on the Seagate?