It's hard to compare TNG and DS9 since they're such different shows from a few fundamental points.
1. The motivation of the crew of the Enterprise is basically go explore the universe, acquire knowledge and lend a helping hand when appropriate. You kinda find out some of the characters individual motives for joining the crew, but the first episode starts out with them getting derailed on the way to a trade station, and ends with Picard going "lets go sightseeing 'round the universe y'all!" Everyone seems real chummy and the Enterprise itself seems like a pretty cushy ship with some nice digs and decent amount of amenities. DS9 introduces Sisqo by killing his wife, thrusting him into single fatherhood, putting him in charge of a fucked up space station at the center of a race war where everything is broken, and making him a deity to a bunch of weirdos he's never met before. Right out of the gate, there's a different weight to the shows.
2. After a while, there's a kind of big difference in the tone of the acting of each show. There are some overwrought moments in TNG, but the later parts of DS9 are filled with semi-campy scenery-chewing by Sisko, Dukat, Winn, and Garak. That isn't really a criticism on my behalf, cuz I really like a lot of those scenes, especially ones with Dukat and Odo. But the shows feel a lot different, especially towards the end in that regard. There's some goofy stuff like Picard getting mad and yelling at a mute, distinguished mentally-challenged version of himself for an hour in TNG, but nothing quite as over the top as shit like the Fire Caves scene at the end of DS9. Bonkers, almost silly, and thoroughly enjoyable.
3. The structure of each show is a lot different. Apart from a few non-consequential storylines and the Borg stuff, there isn't a lot a through-line for TNG. Crusher and Picard occasionally talk about their personal history, Troi and Riker flirt and probably fuck a lot off screen, Geordi stays keeping his dick dry, but for the most part interpersonal relationship between characters aren't the main focus of the show. It's mostly them bouncing around from planet to planet, getting in single-episode adventures that usually ask and answer a question or otherwise lead to an easily summarizable moral. DS9 focuses a lot more closely on the relationships between characters from the start, and keeps it up the whole way through, but besides that the actual story structure changes a lot too - being in a central, static location let the show explore stuff like how tensions between the Cardassians and Bejorans played out and how Sisko handles being an Emissary to a group of people he's almost completely unfamiliar with. From a purely narrative perspective, too, DS9 had a lot less 'contained' stories than TNG, to the point where the end run of the show is like a seven episode arc about The Dominion War. I like that stuff, but towards the end I found the density of it a little overbearing and wouldn't have minded if they threw a story of the week episode or two in there to break it up.
In the end they're both really good, but TNG edges out DS9 for me personally. I think if I did a tally I'd find TNG probably has more 'bad' episodes, but in general I think it has higher highs and lower lows than DS9 and I prefer the lack of constraints and sense of exploration afforded to the crew of the Enterprise
