I think that TOS got it right with just the right amount of friction between Spock, Bones and Kirk. And it worked believably well that science/first officer, captain and chief medical officer would have their personal and professional opinions, but still work together as a team.
The things is that TOS was written more for individual episodes/stories, whereas TNG was closer to a soap opera, with characters personalities developing over several seasons. It doesn't make any sense from any perspective that seven or eight crew members would work and drink and play together with no rubbing up the wrong way. We very rarely even saw the 'mini' jibes that Spock or Bones or Kirk would make.
To this extent, the premise of TNG just wasn't believable, and whilst individual episodes worked very well at times, it was rarely (if ever) because of the development of any character or a building up of a relationship between two.
As Baylor points out, DS9 (which had many faults) was much better in many respects because you could believe the relationships between the characters. Sisko's dislike (perhaps even hatred) of the Maquis wasn't entirely rational, but that's how real people are; they aren't always entirely rational in their objectivity.
As for Guinan, the first time round I saw her in the series it seemed an odd choice, because she didn't fit in with the rest of the crew. Repeated watching made me realise how right a choice she was, for exactly the same reason. There is very much 'the spectator' about her character, and you sense that there is much power and understanding hidden within her, which makes her the polar opposite of Q. I think Whoopi Goldberg is a wonderful actress, and I do think that she is one of the best things about TNG.
