To OP, I wish you'd added a poll to this thread.
Any rate, I'm using Mavericks for my main HDD partition, Snow Leopard on the other half for an older version of Adobe Creative Suite, although I download & create installers of all the new OS's. I do have El Capitan on a 128GB USB stick & have downloaded Sierra. Not particularly impressed with either as they mess up some things with various graphics software & my tablet, plus, the flat UI fad/hiding most of the tools/buttons super irritates me. Mac OS has become so much less overtly functional. I hate having to take the extra bit of time to hunt for things.
Any rate, I'm using Mavericks for my main HDD partition, Snow Leopard on the other half for an older version of Adobe Creative Suite, although I download & create installers of all the new OS's. I do have El Capitan on a 128GB USB stick & have downloaded Sierra. Not particularly impressed with either as they mess up some things with various graphics software & my tablet, plus, the flat UI fad/hiding most of the tools/buttons super irritates me. Mac OS has become so much less overtly functional. I hate having to take the extra bit of time to hunt for things.