I think it's hard to tell. I think TNG has entered a 'sweet spot', similar to the one that TOS had about 20 years ago, where it hit nostalgic buttons but also has a lot of iconic moments and characters that stand the test of time well. DS9 has aged well thematically, as it dealt with a lot of things (war, occupation and terrorism, specifically) that modern shows can't really discuss, BECAUSE they are so relevant right now- it seems too on the nose. DS9 was a bit prescient so it seems forward thinking, but who knows how that will seem in 20 years? I definitely think TNG has a lot of pop-culture cache right now because we all grew up with it, similar to how TOS had cache in the 80s for those who grew up with it in the 60s. Not sure if DS9 will capture the same zeitgeist, but hopefully it's associated with TNG will keep it (and VOY) going for a long time.
ENT, of course, can go and die in a hole for all I care.