To even suggest season 3 of TOS with 50% excellent episodes is better than any other season of STNG is absolutely loopy. Only a masochist would even ruminate about whispering such a thing to an inanimate object in a soundproof room, and probably with lots of padding. My question to you is...how thick is the padding on your walls where you write this?
RAMA
It really comes down to what you enjoy though. TOS, even at it's worst is rarely dry or boring, something that TNG, even at it's best could be.
That's only if you consider, say, a bunch of ten year-olds running around a dining room table while throwing cutlery all over the place "entertaining", while the adults, meanwhile, having a quiet, dignified, and mature conversation around the dinner table is "boring." Sure, TOS, even when terribly written and conceived, seems more "entertaining" because it is colourful and loud and brash and entirely juvenile (when it's bad, I mean.) TNG is quieter, less colourful, less bombastic, more sedate, and more thoughtful - and that may, to some, seem boring, I suppose. And yes, when a TNG episode is mediocre, it doesn't have the crazy TOS incidental score to keep us entertained, or William Shatner's awesome flying kicks, or all those cute girls wearing practically nothing - agreed. Without those silly, juvenile, but effective crutches to fall back on, I guess a mediocre TNG episode would seem more....boring.
But I agree with Rama's sentiment - if your numbers are claiming that Season 3 of TOS is superior to, say, Season 3 or 4 (or 6) of TNG, then your numbers are, in fact, lying. TOS season 3 is a huge, huge letdown after the first two mostly fantastic seasons, except for a handful of great episodes. When it's bad, it's really, really bad, while, again, still seeming very "entertaining" - 'cause, again, of all those colours and lights and nifty sounds and overacting and fist fights and silly costumes and girls in sexy short skirts and things. It always seems like a lot of cool stuff is happening, though, sure, even when the writing feels like it was written by a 6 year-old.