The PANTHER website offers a tool to obtain the GO-based overrepresentation of a gene list (the analyzed list) versus a reference gene list. After entering both these lists, the tool asks to choose between the Fisher's Exact or Binomial tests.
I guess that the convenience for one or another test would depend on the number of genes to analyze. If that is the case, which would be the ideal or advisable rank of gene numbers in both analyzed and reference lists (or their ratio) for each type of test?
(In particular I am working with a list of around 150 versus a reference list of around 2000 genes).