As much as I like supporting actors like Rene Auberjonois and Armin Shimerman, who can shine through the makeup and portray their characters realistically, I have to disagree regarding the main casts. I think they are about even as far as acting ability; from TNG you have excellent actors in Patrick Stewart, Brent Spiner, and LeVar Burton, generally good acting in Michael Dorn, Marina Sirtis, and Jonathan Frakes, And "good enough" from the rest.
In DS9, you had great acting from the above mentioned Auberjonois and Shimerman, though both could ham it up as well. Passing performances by Avery Brooks and Nana Visitor were the norm but they were both known to shine as well as fall flat. Alexander Siddig is an enigma; he was so good at being annoying that one might dismiss him before realizing that he was the perfect choice for the role. Poor Cirroc Lofton, like Wil Wheaton, suffered from the "kid surrounded by grownups" typecasting that often kills a child star's career. Both are decent actors but were never allowed to grow very much with their roles. And again, the remaining cast were neither great nor horrid.
In short, both casts had a range of acting ability, and even the best actor can't always rescue a bad script or director. But to say one is hands-down the best compared to the other is, at best, blind favoritism ("I liked one show better than the other so the other cast must suck").
Q was pretty clearly designed as an antagonist and foil for Jean-Luc Picard, and he never made a lot of sense in the other series. He was brought into those series, like the Borg, for ratings stunts. And it showed.
Thankfully, the writers of Enterprise never panicked and pushed the Q button the way Voyager's did. The Borg make a questionable and continuity-challenging [1] appearance on Enterprise, but Q never does.
I watched all of Enterprise. It...gets better in Seasons 3 and 4. That's about all I can say. The first season is pretty bad. Season 2 has a few good episodes. In Season 3, things start to pick up a bit, and Season 4 is legitimately interesting. The show never quite reaches the heights of TNG, DS9, or TOS. But it gets pretty good. I'd only recommend watching it all the way through if you're ready to wade past the early crap, though.
[1] This is kind of a mixed bag. The explanation for their appearance stems from the events of Star Trek: First Contact, in which a small detachment of Borg drones are left behind on Earth in the 20th Century. So the timeline has been altered a bit, and hence, those remnant Borg show up in Enterprise. On the flip side, you'd think that an early encounter with the Borg would have stuck in everyone's memory a little bit, and that Picard wouldn't have been shocked upon first encountering them. The episode acknowledges the issue, at least, and attempts to arrive at a workaround. The fix is clever, if not entirely satisfactory.
Ugh, don't remind me. That was the worst. Why can't shows just acknowledge that makeup and effects change over time, and leave well enough alone? Augment Virus was Enterprise's attempt to cave into fans' demands that Star Trek offer an explanation for the TOS Klingons. If you ask me, Star Trek should've just hand-woven that subject indefinitely.
DS9 handled the matter much more effectively in "Trials and Tribbleations." Someone asked why the old-school Klingons had smooth foreheads, and Worf replied "We don't like to discuss that with outsiders." Boom. Perfect explanation. Funny, clever, and hand-wavy. Done.
In DS9, you had great acting from the above mentioned Auberjonois and Shimerman, though both could ham it up as well. Passing performances by Avery Brooks and Nana Visitor were the norm but they were both known to shine as well as fall flat. Alexander Siddig is an enigma; he was so good at being annoying that one might dismiss him before realizing that he was the perfect choice for the role. Poor Cirroc Lofton, like Wil Wheaton, suffered from the "kid surrounded by grownups" typecasting that often kills a child star's career. Both are decent actors but were never allowed to grow very much with their roles. And again, the remaining cast were neither great nor horrid.
In short, both casts had a range of acting ability, and even the best actor can't always rescue a bad script or director. But to say one is hands-down the best compared to the other is, at best, blind favoritism ("I liked one show better than the other so the other cast must suck").