The Last Stand of the Wreckers is the greatest Transformers story ever told. It has two sequels: The Sins of the Wreckers and Requiem of the Wreckers. "The Wreckers Saga" collects all of these and is cheaper than buying them seperately, so if you just want one book, I recommend that.
More than Meets the Eye and its' sequel Lost Light are the big ones everyone raves about. You can just go MTMTE Vol. 1-5, Dark Cybertron (the "Thrilling 30th" anniversary story) Book 1 and 2, 6-10 and then the Lost Light trades. Vol. 1 has a one shot that launches both that and its' sister book Robots in Disguise, which is less good, but gets better when it continues as The Transformers, and later on, Optimus Prime. If you are dipping into MTMTE, I highly recommend the prequel story "Chaos Theory", which was printed in Transformers (2010) #22 and #23. It is EXCELLENT, skipped by many reading orders, and lays the groundwork for a lot of the story beats that come later on.
I personally was a big fan of ROM vs. The Transformers: Shining Armor as a big, punchy, splashy crossover as well. It's told from the POV of a new character so you don't need to know much.