It really depends on each model.
-21-22's have really ugly battroid, those are fighter for me. (17S falls in this group)
-VF-11 super fighter.
-19S is now diplayed in battroid. YF-19 fighter is the best mode (with fold booster)
-VF-1 is the only model (IMO) that covers all the modes neatly. 1J battroid GBP (and stand-alone), 1S,J,A super/strike fighter (and stand alone), 1D gerwalk.
-VF-4G fighter or battroid.
VF-25-27-29... those flying turkeys...