Frankly, all the treks are similiar.. seasons 1-3 meh to blah, seasons 4-6, pretty good, season 7 depends.
Even Enterprise , who had a much shorter run, knew it was in danger of cancelation and after season two , kicked it up a few notches.
My list if it "only" had 5 would be, and Im regulating to "space" shows vs "scifi" shows.
3. Star Trek Voyager, I really think this was some of the most worthy moments of trek history from Seven of Nine to the end. It was truly a treat to see Sevens growth, the interactions of the crew around having a borg on board, plus you have to admit the show was ten times better when they changed antagonist to the Borg. The show really started off slow, but built, just like TSG and DS9 in my opionion, however overall I would rate Voyager as slightly ahead of both of those in its overal content. I just cant get over how terrible the start of ds9 was, I know some of you will disagree, but there is a reason they made as many changes as they did.
Not on my list,
Dr Who.. its more scifi, then space based scifi, so it would be in my top 5 of my whole complete list for sure, as would star trek TOS, but if your judging a show by its ships, the Tardis, is more a vechicle to a destination and never a vechicle you lived in , for the show purpose anyways.
B5, story arc aside, I just dont think this is a top 5 show, either in the space side , or full list side. It never drew me in like other shows, I struggled to get through them at times. There is a reason you share story writing responsibilites at times, fresh perspectives, do help!
DS9, early DS9 was just the worst of trek IMO only, it grows, it grows dramatically , but I cant get past those first couple of years, the worst of DS9 is far more horrible then the worst of TSG or Voyager.
TSG, This grows as well, from borg/picard onward, the show is much better. There is a episode, where they focus on lesser officers for a whole show, its really quite unique in the trekverse, I wish TSG highlight moments were earlier and more often, but the best of TSG still holds well. .