The ballades have always been on roughly equal footing in my list of preferences (not so the scherzi or impromptus, of which Chopin also wrote four each (counting the Fantasie-Impromptu as an impromptu) - preference lists there running 4-3-2-1 and 3-2-FI-1 respectively); if pressed, I'd probably name the F major as my favourite, and while I do like the G minor, the fact that it is the most overplayed of the four by a wide margin probably pushes it to the bottom of the list. The A-flat major and F minor are probably more or less even between the two.