I choose Sinclair. He might not have been in the best season, but I prefered him (and the actor) above John Sheridan. He had a powerful and calming presence.
But this answer wasn't truly honest, I just think he deserves some credit, even if, in the long run, I much prefer Londo Mollari and G'Kar. These two were amazingly crafted and played characters.
Garibaldi is a close follow-up, as would be Bester.