I'm another one who grew up with TOS all during the 1970's and early 1980's, so TOS will always be my favorite. I've seen the episodes so many times by now they are like old friends who I can always count on to be there for me.
I'd list DS9 a very close second, though. I didn't really warm to it at first but it definitely grew on me. I do believe that Ben Sisko is still my favorite of all the captains, though. If I had to pick one to serve with he'd be my choice.
I love TNG, too, but it just seemed a little too "perfect" to me. I do have a list of favorite TNG episodes that I still rewatch on occasion but I can't ever imagine it being as important to me as TOS is.