Originally posted by 0°Mandalore°0
By 'several Force-users' you mean only Jedi, correct?
That is not as easily a cut-and-dry question as one makes it out to be. On the one hand, yes, only two Jedi Masters, in the words of George Lucas can "compete" with the Galactic Emperor and have demonstrated the necessary skill and power to defeat him in single combat; Masters Yoda and Windu. But, objectively speaking, that Windu is included in that list -- indeed, he came closer to ending Sidious's life than Yoda himself did -- brings another question into mind: does one necessarily have to be stronger than the Emperor to kill him? Sidious's own words from the Telos Holocron seem to indicate that the Galactic Emperor supports the out-of-universe "Any Given Sunday" rule (the old lesson that any foe can be defeated if given the right circumstances): "Yes, Vader remained strong in the Force, but strong enough to succeed me? Never. Granted, he was strong enough to kill me. But that only lasted for so long." -- page 170.
Despite Windu's formidable skill, the novelization quite explicitly states that the Supreme Chancellor initially held the advantage. He was faster and more agile than Windu, which is the likely cause of why Sidious was able to so effortlessly obliterate three of the most senior and capable Jedi Masters at the time (indeed, they were considered some of the very best ever). But, we all know the nature and fundamentals of Vaapad, they've been discussed thoroughly. And certainly, Windu has never demonstrated the extent and control of the Force that the Emperor has.
In terms of raw power, one can readily state that Anakin Skywalker and Luke Skywalker both possess raw power well in excess of the Galactic Emperor's. Despite his lackluster performances, one can also assume that Darth Caedus and Kyp Durron also compare to Palpatine on a level of raw power. Mace Windu and Yoda? That would require further debate, because one could assume that -- despite the fact that one can always learn new Force techniques -- after nine centuries, Yoda had reached much of his own personal potential, whereas the Galactic Emperor most assuredly did not (Lumiya offers in Legacy of the Force that the Emperor's power was "limitless" and Mara Jade Skywalker, despite being intimate with Luke Skywalker, refers to the Emperor's reserve of Force energy as "vast"😉. Windu? Once again, we know that he is a Jedi Master of nearly peerless talent -- but does he compare on a level of raw power? Perhaps.
In terms of acquired knowledge, Palpatine has demonstrated a deeper and more profound knowledge of the Force than any other being in the mythos. Obviously, his knowledge is not completely infallible. He still has learned and invented new techniques, and if one can assume Darth Plagueis truly possessed the power he is reputed to have (which evidence points to as fact), Sidious did not know it. I would argue that only Yoda and the collective Ancient Sith seem to come close in terms of depth. As far as range, only Jacen Solo and Luke Skywalker can compete.
In terms of acquired power, knowledge, and skill, I would have to say that the following could be argued to be on a level with the Emperor: Luke Skywalker, Jacen Solo, Kyp Durron, Marka Ragnos, and Exar Kun. Perhaps, as well, Sekot. And insofar as who could likely defeat him? I'd say that would only go to Luke Skywalker, post New Jedi Order.