I think most people agree that TNG is either at the top, or close to the top for best series. There's also a smaller, diehard group that think DS9 is the best trek (myself included).

TNG is more adventurous where the crew is always on the side of morality and reason, and use wits and principles to overcome obstacles. Every episode is an adventure, and each adventure varies greatly from saving a planet from destruction or saving someone from their own mind. DS9 has larger, darker story arcs and more of a "sitcom" feel (in the best way possible) where the focus is more on the characters rather than the adventure. The episodes vary greatly in terms of theme, you could have an episode where you're laughing every 2 minutes from the sheer silliness, or witness the most psychologically gut-wrenching thing you've seen in a long time. You can't go wrong with either, and both have a bit of a rougher first couple seasons before they hit their stride.

As far as more recent trek, I enjoyed pretty much all of them but I would say strange new worlds is probably the cleanest and best for a new person. Lower decks is absolutely incredible but is more of a love letter to all the previous shows so you won't get as much out of it as someone who has seen everything.