My favorite would be Corum Jhalen Irsei, the Vadhagh Prince in the Scarlet Robe. Possibly because "The Swords Trilogy" was the first of the Moorcock books I read, possibly because he was the last of his kind (for the most part), but most likely because the device of the Hand and Eye and his summoning his last enemy to fight his next enemy.
Initially, I didn't like the following three books as well, but after a few years I began to read all six together as a complete story instead of as the original three and the derivations. I am drawn to his personal tragedy, as someone said earlier.
Elric is close, close, close second. I was intrigued with the glimpse of him (and Erokese, and Hawkmoon) in the scenes of The Vanishing Tower, and was really drawn to the idea of Stormbringer and the tragedy inherent in elric's saga.
Actually, I think some of the big "unifying moments" for the Eternal Champion are in the first three Corum books, not only with the three incarnations fighting together at the Vanishing Tower, but as Corum and Jhary pass through universes projected like quickly-changing movie screens looking into the lives of different incarnations.
I highly recommend reading the Corum books again.