Main difference for me was the acting, with TNG losing out.
Stewart was great, perhaps the best actor of all the series. Spiner was OK. The rest of them couldn't act their way out of a turbo-lift.
OTOH, Shatner was, well, Shattastic. Nimoy was excellent and more--definitive. Kelley was really good when awake, and more importantly, fun to watch. Doohan was outstanding when given material. As for "the rest", well, Koenig was actually a pretty good actor, and Takei likewise. Nichols was surprisingly strong in her few moments. Majel, well, she was actually better in TNG.