I grew up on TOS. The three musketeer thing between Bones, Spock and the Capt. is classic. Truly a paradigm shifting event.
I have all five series on DVD.
TNG rubbed me the wrong way...I don't know - maybe too cushy, smug, and politically correct.
Voyager ranks a strong second IMHO...strong character development, and I'm in love with Janeway / Kate Mulgrew...what a woman!
I throughly enjoyed Enterprise, and was truly saddened by the series demise.