Gold is for servers. I have one and it's supposed to be extra reliable.
However it is kind of loud and annoying. Thank goodness I only use it to run back up's at night.
WD Blue is fine for most people and WD Black is a high performance HDD.
I don't really care if my HDD's are high performance. That's what my SSD's are for.
I have reliable 5400RPM WD Red and WD Gold HDD's in my System.
TBH I don't notice any performance hit using a "slow" HDD for long term bulk storage. Documents, Pictures, Videos, Downloads, Music.
Western Digital, Hitachi, Toshiba and HGST (owned by WD) are good drives.
I avoid Seagate. Every Seagate drive I have owned has died.
In fact, the only drives that have ever died on me have been by Seagate.
Other swear by them, I swear at them.
A 256GB SSD is big enough, 120 is completely too small.
I had to constantly manage it to keep it from filling up. Then it died because I had it too full for too long.
I have a 400GB Intel 750 PCIe for Windows, a 500GB Samsung for Steam games and a 500GB Crucial for other games.
Although the PCIe drive is faster, It's really only faster for working.
When I edit video or big files, I temporarily copy the file to the Intel and work on it there.
99% of the time I can't tell the difference between a 2,100 Mb/s PCIe drive and a 500 Mb/s SATA III drive, IRL.