I don't know if it is the best, but the most employed catalytic system may well be the dolomite limestone. I recommend you reading this paper: "Hydrogen-rich gas from catalytic steam gasification of municipal solid waste (MSW): Influence of catalyst and temperature on yield and product composition".
In my case, I used the combination of activated carbon and olivine or dolomite (as bed materias) to remove tar in producer gas. although activated carbon is more expensive than other mineral materials (olivine and dolomite), if tar removal system (additional system) bulid, the use of activated carbon as primary method is better than secondary method for tar removal.
I recommend reading this article that answers your question:
Abu El-Rub, Z., Bramer, E. A., & Brem, G. (2004). A Review of Catalysts for Tar Elimination in Biomass Gasification Processes. Ind. Eng. Chem. Res., 43, 6911-6919.