My first run through on DVD, I started with Season 4 because Worf joined at that point. After I'd purchased/seen Seasons 4-7 and loved them, I went back and got 1-3. After viewing those (I'd seen most of 1-3 first run) I realized I missed a lot and then watched 4-7 again. It was an even more enjoyable experience, seeing how the show grew and improved.
I'm currently doing TOS with the kids (we took a hiatus mid-season 2 since August) and TNG on my own (up to about the second ep of season 3, the kids REALLY don't like TNG anymore because they detest the movies....who can blame them?).
Bottom line: start from the beginning: it's a much richer experience!