yeah everyone has different preferences when it comes to trans fluid. I like to run the 15w40 rotella in my e50's and i like to run the 10w40 'valvoline motorcycle oil' in my ZA50.
you get a little more slip on the rotella
in my experience from least-most slip:
ATF type F
ATF dex/merc 3 (very slightly more slip, imperceptable on most setups)
0w20 mobil one (my wife's car uses it so i have it around)
10w14 valvoline motorcycle oil - now the difference between the 0w mobil one and the valvoline motorcycle is that the clutches in the 2 speed will 'stay locked' better with the valvoline, the 0w they will grab about the same but especially when its warm it will downshift sometimes when you dont want it to which gets annoying
10w40 car oil generic pennzoil- sometimes slips more sometimes slips less, i don't like using this vs the motorcycle oil because it changes a lot with temp. feels great when its cold but gets grabby hot.
15w40 rotella - i like this a lot in the e50, i also like that you can leave the springs a bit less pressure and get the same effect which means less wear and tear on the clutches
gear oil would go above this- 80w90 gear oil- personally i have avoided this because i've never needed it