Anymore, I've started considering the following as occuring in separate universes:
3. TNG(and its movies)/DS9/VOY
Perhaps created by different time travel muddling on the part of our heros, for example, the events of TVH created the "TNG" universe and FC created the "ENT/JJ" universe. I split TWOK-TUC from the rest of TOS because the look and feel seems quite a bit different to me that what came before, it also fixes the sloppy continuity errors and references that occur between the two. I stuck ENT into the JJverse since one would think, even though I know it is impossible, that some reference to it should have occurred in TNG if it were truly part of that universe. Also, the look of Kelvin's bridge reminds me of the NX-01 and the NX-01 was large enough that the larger JJverse ships are a more natural design evolution.
But ENT was
referenced in TNG in the ENT episode "These Are The Voyages..." Sure, the episode may have sucked, but that episode was pretty much another TNG episode. Therefore, ENT and TNG took place in the same timeline.