For G1, I'd say Metru build was the almost perfected Toa build. They were full of articulation, while keeping some nice technic engineering, including the beloved gear function. They had solid coverage, nice functions, and kept the Bionicle feel of the prior three years. In addition, they had a great price range.
However, when adding G2 into the equation, I think the Masters fixed all of the big flaws with the Metru build. And with that being said, I prefer both the Master and Uniter build. I feel like these greatly improve on G1's building style, but each one of them still have minor flaws.