What is the best way to make use of the money I give to charity?

Every year I set aside $500 to donate to charity; sometimes I exceed it, but I never donate less. Typically, I donate a certain amount to 3 specific charities, and then use the rest throughout the year as needed for things I care about. Lately I have been wondering if this is the best way to utilize my money and make the biggest impact.

Would it make a bigger impact for animals (what 80% of my money goes to) if I just spent that $500 among the 3 charities I support the most, pick one charity a year and donate that $500, or continue my piecemeal donations throughout the year?

Your suggestions are greatly appreciated.

General question.