I watched the earlier Star Trek series and enjoyed them very much; however, I have not begun watching Discovery as yet, largely because I was already invested in other series when it first began and just never got around to it. I do believe that I can catch up with it on one of our free streaming channels, and now that this thread has jogged my memory I shall take a look later on.
Of all the previous Star Trek series, Voyager was/is my favourite, I think because it departed from male captaincies to having a female captain and was set in another, previously unexplored universe. That doesn't mean to say that the other series weren't good, though. While the first series was ground-breaking and took us to new heights, I liked STNG a bit more, I think because Patrick Stewart was enigmatic and portrayed a convincing starship captain.
Deep Space Nine was also good, but I don't hear about it too often during 'Trek' conversations