At the moment there are no better alternatives that satisfy all the observations. If you try to replace General Relativity with something like Modified Newtonian Dynamics (MOND) [1], then you can get good fits to galaxy rotation curves. However, there are many sources of astronomical/cosmological data that will not bend to alternative gravity models, e.g the precise fluctuations of the cosmic microwave background put stringent bound on the matter components of the Universe.

[1] https://en.wikipedia.org/wiki/Modified_Newtonian_dynamics#Ou...