This is a hard one as far as which is the best. I really thought TNG-5 was strong and had a nice run. I mean putting out 26 episodes a season can't be easy yet I thought TNG-5 had not only a consistent run but the weakest episodes, like season four, weren't awful just average. You had a nice mix of different story styles. I enjoyed Ensign Ro, Silicon Avatar, Disaster, The Game, Unification, Hero Worship, Violations, Conundrum, Power Play, Ethics, Cause and Effect, I Borg, The Next Phase, The Inner Light, Times Arrow. And even the season's worst episode--Cost of Living--is not unwatchable. It just has a rather dull B plot with the metallic parasites but the A plot while far from great is not bad and I thought the scene between Alexander and Lwaxana about growing old was moving.
Then you've got DS9-5. I thought this was the turning point for the series. To me the whole Dominion conflict is what drew me into the series and when it was at its best. I think it is a solid season but I enjoy probably less for the individual episodes but the overall shuffling of the players in the Trek universe and the bold shake-ups it committed to--the Dominion coming back into things by absorbing Cardassia, the Maquis being annihilated, the Klingons returning to the Khitomer Accords, Weyoun becoming the face of the Dominion, Dukat becoming a power player once again, the addition of a Klingon perspective on the War with Martok, the collapsing of the wormhole no longer being an option, Bajor signing the non aggression pact to stay out of harm's way, Sisko abandoning the station and the beginning of the Dominion War.
The interesting thing is those events were pretty much confined to three or four big event episodes which not surprisingly are my favorites including Call to Arms. But for me DS9-5 wasn't perfect. It had some truly awful episodes that TNG-5's worst couldn't come close to--Looking for Par'Mach, Let He Who is Without Sin, Ferengi Love Songs for instance. Althought none of the best of TNG-5 really came as close to the best of DS9-5--In Purgatory' Shadow/By Inferno's Light, Trials and Tribble-ations, In The Cards, Call to Arms.
I found The Ship, while seemingly loved by many, to be overrated. The Outcast romance or The Perfect Mate romance stories were superior to A Simple Investigation which was an overall dull episode. TNG's Power Play was far more engaging than DS9's The Assignment which was a merely average episode. "Dr Bashir I Presume?" was a middling episode saddled with a lame B plot that comes nowhere near the interesting discussions "Ethics" stirred up. I appreciated that "Soldiers of the Empire" gave us insight into how Klingons were dealing with the Dominion incursion into the Alpha Quadrant but felt it retreaded too much Klingon milieu and so was quite average.
The season was also plagued by romantic experimentation that I could have cared less about--Worf/Jadzia, Rom/Leeta, Moogie/Zek, Quark/Grilka. The Kira pregnancy culminating in that pointless B-plot in The Begotten did nothing for me nor did Shakaar's appearance in that episode.
I don't know I flip flop a lot between which is the better season but for now I'll give a very slight edge to DS9 because I enjoyed myself more from week to week with TNG, TNG wasn't as ambitious or epic in its storytelling whereas DS9 in certain weeks thought BIG in season five.
VOY-5 to me was a step down from season four. It was all over the place with enjoyable stuff like Night, Timeless, Bride of Chaotica, Dark Frontier, Think Tank, Relativity, 11:59, Equinox but it had some pretty boring hours like Gravity, Juggernaut, Extreme Risk, and bad stuff like The Fight, The Disease, Once UPon a Time, Course:Oblivion, Nothing Human. And while In the Flesh is a decent episode I thought Species 8472 were the wrong aliens to use since it ruined them for me by turning them into humans in the form of Boothby. I always thought it might have been a better episode for DS9 featuring the Founders.