"It took a really long time for Nick to work out Sidious' fighting style, and he has a style that's constantly changing. His style is one in which you'll never get the better of him. It is ambiguous --- he'll fight less than you and draw you in; you're a sucker if you think you're going to better him. Sidious is a master of every weapon and every style."
Nick Gillard
Take that as you will.
Sidious' lightsaber form continuously changes during the battle depending on his stance, environment, enemy and even if he is winning or not. As said before he tends to draw the opponents into thinking that they have beaten him, and then blow a fatal strike to them. He is ambidextrous so he can change from left handed to right handed and have no difficulty swinging to pushing on strength.
I should also add that Sidious has one of the most unusual lightsabers I have ever seen, most likely for it to be able to be used on every form.