I would opt for the Birch. without seeing it.

poplar left natural is too green and maple is too white, also very hard, unless you want it that light. did you use a waterbase poly? or a yellowing oil base?

certainly they don't need to match, but what is the style you are going for? will you be adding yellow paint/furnishings? that will bring out more yellow, with lighting too.

Thanks! The floors were pre-finished and I'm not sure what that means for poly/oil? I don't plan to use yellows on walls/furniture because the floors bring out so much yellow already, especially with the LED lighting in the kitchen. Finding birch baseboards seems to be much more difficult than poplar or maple, but may be worth putting in the extra effort to source.