Anything from the recent Nvidia line (GTX 1660 and up.. not the 1650) objectively has the best hardware-based h264 encoder in the consumer market right now with the turing NVenc encoder. Which card you go for depends on how much of a need you have for other things (i.e. gaming) -- they all have the exact same encoder on board, and all will easily handle most use cases of OBS.
Previous generations of Nvidia cards also have NVenc on them, but of lower quality just due to generational advances made.