Frankfurt, for several reasons:
1. It is sometimes ranked among the top 100.
2. Frankfurt already sent people to top 10 PhD programs in the US. See e.g. him
Economists - Christian Matthes - Federal Reserve Bank of Richmond
I am not aware of anybody from Alicante managing to get into a top PhD program.
3. You will benefit from Frankfurt in terms of location because it's where the ECB is.