1. Luke Skywalker (NJO and beyond) was able to move his saber so fast that it was invisible
2. Tulak Hord (was stated to be the strongest ancient Sith with a saber and also stated that compared to the ancient Sith the KoToR Sith were children playing with toys)
3. Darth Bane (with under a year of training he was able to beat Kas'im, the best saber master of his era, and was able to toy with Sirak, the second strongest student in the academy. In his prime Bane possessed Orbalisk Armor which feeds adreneline into his body and also makes him invulnerable to lightsaber attacks - only his head remains unprotected)
4. Kol Skywalker (went up against about a dozen Sith at once and killed at least 7 of them)
5. Darth Sidious (from Dark Emperor, was stated to move so fast that he's a blur)
6. Kyle Katarn (with no formal training beat 7 Dark Jedi (5 f them one on one, tow of them he beat at the same time, though). Beat Desann when even Luke was unable to).
7. Exar Kun (Makashi Master, invented Double Bladed Lightsaber, beat Master Vodo as a Padawan and pwnd him as a Sith Lord)
8. Kas'im (was stated to be the best saber master of his era and possible the best of any era (includes the era of 1000 bby and earlier). Moves as a blur. Could possibly beat Exar Kun)
9. Mace Windu (inventor of Vaapad and only Vaapad Master in the sw universe, Vaapad is the Ultimate Form, Mace also has his unique Shatterpoint ability and bested ROTS Sidious in a saber duel)
10. Anakin Skywalker/ROTS Darth Vader (when his mind is clear and he's thinking properly he is able to pwn Dooku, beat Cin Drallig after fighting many other Jedi, though if he isn't thinking clearly, as in his fight with Kenobi in ROTS, he is behind a few other people).

Honorable mentions: Yoda (could maybe be above Anakin, not sure, very, very close), ROTS Kenobi (a bit further down the line), Dooku (same as Kenobi), Maul (further down than Yoda), ROTS Darth Sidious, EU General Grievous, Darth Revan, Darth Malak, Darth Traya.

4. Count Dooku and kar vastor

Kar Vastor is nor a saber wielder.

I have researched this topic and found out General Grevious Killed 23 Jedi And Fought Mace Windu and tied him

Actually, the General grievous comic states that he's killed over a hundred Jedi and he never stalemated Mace Windu, the fight you are referring to happens in Labyrinth of Evil and Mace wins, but it is pretty close.

Vader isn't the most powerful Sith ever, he hardly makes the top 20, Darth Nihilus, Sidious, Exar Kun, Darth Revan, Darth Bane, Tulak Hord and Marka Ragnos are above him for sure, they are the strongest.

Darth Maul Darth Maul Is the only person ever to be seen wielding a Saber staff not only that But Darth Maul at one point just about beat Darth Sidiuos In a Lightsaber Battle The story goes Like this

Darth Maul Darth Maul Is the only person ever to be seen wielding a Saber staff not only that But Darth Maul at one point just about beat Darth Sidiuos In a Lightsaber Battle The story goes Like this

1. Maul almost beat Sidious, making Sidious above Maul. Also, Maul is NOT the only one to wield a double bladed saber, Kas'im does, Exar Kun invented it, Bastila Shan, Darth Bandon uses one and he isn't even that great. There's a lot more people, too.
http://starwars.wikia.com/wiki/Double_Bladed_Lightsaber

Also in another book I read Obi-One states that Count Dooku Is stronger Than Darth Maul He didnt neccesarily Say In Lightsaber Usage or the force it jus says hes More Powerful

Not saying I disagree with that, but I'm just wondering which book you're referring to?