The problem is, it very much involves the Klingons...at least in the battle scenes.
Well, yes, but you don't actually see Klingons as I recall, just their ships. And this isn't a Klingon-centered episode really, so I'd say it counts.
For full disclosure, Yesterdays Enterprise
is in my all time top 5. I love this ep and highly recommend it. But within the parameters set down by the OP, it doesn't fit the request. I'm not trying to pick nits here, I'm just pointing out the fact that it was actually a very
Klingon centric episode even though actual Klingons were never scene, just their ships. In the timeling created by the E-C's arrival, the Fed was about to lose a war to the Klingons that should have never started in the first place. Capt Garret was killed by a Klingon attack. I could go on, but you get the idea. The entire plot of Yesterdays Enterprise
is woven around the Klingons.
I forgot to mention Reunification. As far as I remember it doesn't include Borg, Q or Klingons, and there's a really good performance from Leonard Nimoy returning as Spock.
Another great ep. The problem is the Klingons play a very important role in Part II and they, or their ship, have plenty of screen time.
I guess my vote would have to go to Sarek.
It has a little of everything. Good TOS cross over. All of the main cast gets some time, and Stewart still gets to show off his acting chops. The Perfect Mate
would be a strong alternative. Normally I would put The Inner Light
in contention as well, but if you are chosing just one TNG episode to watch, it might be a little too Picard centric.