Luke Skywalker – Luke is the most powerful Force User we have ever seen. He is head and shoulders above all others at this time. The amazing things that he has been able to do dwarf everyone else, and also we know that he has the potential Darth Vader had but didn’t destroy his body the way Vader did.
Darth Sidious – Emperor Palpatine was, according to canon, the most powerful Sith ever, with the exception of Vader if his power was realized. As such we have to give him a high position on this list. Palpatine was defeated by Luke in a test of both Lightsaber combat and Force abilities though and was found lacking. Thus I put him right below Luke in terms of sheer power.
Yoda – I met him in a swamp down on Dagobah, where it bubbles all the time like a giant carbonated soda… Y-O-D-A Yoda. We have to give it up for the muppet master who taught us all that size matters not. Able to match Darth Sidious blow for blow, and even overpower him in a pinch Yoda only “lost” to Sidious due to his small stature. As such Yoda must rank in on this list.
Darth Vader – Vader was said to be somewhere around 80% of Sidious’ power, and he would have been stronger if he had not ignored the benefit of the high ground. While he is no slouch, he simply can’t rank any higher than this on my personal list.
Nomi Sunrider – I have to give Nomi her proper respect. She is a little known character outside of the high EU circles but she is one bad mamma jamma. Nomi Sunrider was able to cut a Dark Sider off from the Force until they completely repented, a feat normally requiring a whole group of Jedi Masters. Had she been the main character in KoTOR II she would have mopped the floor with Sion and Nihilus with ease.
Hardcore fans will note a couple of names are left off this list, the reason for that is because there are specifically two I did not consider as valid entries. That is because one is a planet and we have no clue what the other is supposed to be. That would be the planet Zonema Sekot and the creature known as Abeloth. I don’t count them under the general term of Force User.