I guess I should add my two cents to this thing...
If you're playing as a...
HUmar - As many have mentioned, this always appears to be the one that is used by newcomers to the game (even I used it). Since the HUmar is always going to deal Physical damage, try this button scheme...
B - Resta
A - Normal Attack
X - Heavy Attack
R+B - Moon Atomizers
R+A - Jellen/Zalure (whichever one)
R+X - Jellen/Zalure (whichever one)
I found this to be very useful, so its just my opinion.
HUneweral - Havent played much with this type, but, In my opinion, you should ALWAYS have some way to access Shifta and Deband quickly, whether its part of your button scheme or not.
HUcast - assign two of your traps to any of your buttons. As far as weapons go, have at least one mechgun type, one sword/partisan type, and one double saber type weapon.
HUcaesal - Same thing as HUcast. However, your main focus on weapons should be Double Saber weapons since they, supposedly, have the fastest battle animations. Also have a Red Handgun/High Hit % Diska with you incase going "up close and personal" isnt working.
And we all know the disclaimer by now...
"They're all just my opinions."