He describes himself as powerless in his current spirit form, so clearly he was far more powerful when he was alive.
As a spirit he is able to force push Vodo down to the ground from halfway across the galaxy, heal Kun using the darkside, instakill a dying King Ommin, use the force to pull Kun's saber away (might not seem like much, but if it was that easy to force pull someone's saber away, there would never be saber duels; one of the basic lessons that jedi padawans learn is how to repel this, the fact that Kun couldn't stop Nadd from doing this is pretty impressive), cause an avalanche (granted it was a chain reaction).
We know that he was in possesion of sith artifacts such as Sadow's ship, sadow's amulets, most likely the orbalisk armour that Bane discovers in his tomb years later and most likely a bunch of other stuff. We also know that he knew sith magic, most probably King Adas' holocron as well and he most likely was able to access it if he did actually have it. He also likely killed Naga Sadow. I'd say logic points to Nadd winning this.
Here's the list:
1. Luke Skywalker.
2. Jacen Solo.
3. Darth Krayt.
4. Kol Skywalker.
5. Raynar Thul (Killek powered).
6. Darth Sidious.
7. Zenoma Sekot.
8. Kyp Durron.
9. Darth Revan.
10. Darth Bane.
11. Marka Ragnos.
12. Darth Nihilus.
13. Exar Kun.
14. Naga Sadow.
15. Simus.
16. Ludo Kressh.
17. Darth Traya.
18. Darth Sion.
19. Darth Malak.
20. Darth Bandon.
Potential to be on the list: Cade Skywalker, Jaina Solo, Nomi or Vima Sunrider, Zayne Carrick, Darth Zannah, Bastilla, Ben Skywalker, Allana Solo, Leia Organa-Solo, Darth Talon, Shado Vao,
Unknowns who could possibly make the list: Adas, Xendor, Ajunta Pall, The Dark Underlord, Tulak Hord, Roan Fell (and potentially Sia), Lord Hoth, Lord Farfalla, Darovit (potentially), Kiel Charney, Freedon Nadd, Quordis, Kaan, Kopekz, Seviss Vaa, Darth Nihl, Darth Stryfe, Darth Wylock, Wolf Sazen.
Those who just missed it: Yoda, Ulic-Quel Droma, The Exile, Mace Windu, Anakin Skywalker, Odan-Urr, Vodo-Siosk Bass, Thon, Dooku, Kyle Katarn, Ka'sim, Githany, Lady Lumiya.
Don't think I missed anyone.
Originally posted by Kas'Im
Here's the list:
1. Luke Skywalker.
2. Jacen Solo.
3. Darth Krayt.
4. Kol Skywalker.
5. Raynar Thul (Killek powered).
6. Darth Sidious.
7. Zenoma Sekot.
8. Kyp Durron.
9. Darth Revan.
10. Darth Bane.
11. Marka Ragnos.
12. Darth Nihilus.
13. Exar Kun.
14. Naga Sadow.
15. Simus.
16. Ludo Kressh.
17. Darth Traya.
18. Darth Sion.
19. Darth Malak.
20. Darth Bandon.
with no effort at all, he learnt everything from sadow and single handedly conquered onderon and became king.
and personally id put nadd avoe exar kun, as a weak spirit, triggering an avalanche, pushing some one from another part of the galaxy and being able to instanly heal a dying man is wtf man, imagine what you can do if you are in your physical body so heres mine.
and dont forget zukas quote "he was far worse than revan and malak ever were" and the mandalorians do their studies and they know how to judge their enemies.
1.Mr luke and mr anakin at his peak
2.darth nihilus
3.freedon nadd
4.DE palpatine/exar kun
5.jacen solo
6. kyle katarn
7.EU darth vader (bias)
and darthsith19, kiling nadd in his physical form wont be easy, already he did impressive things as a spirit, exar kun needed a body to do his shit in JA, palpatine could drain others and also needed a body to do his shit, but nadd was different, he did things as a spirit
Only Anakin never made itto his full potential, Luke is the best right now, and said Jacenis on his way to best him...
from wikipedia...possible spoilers ahead...
Stronger than Luke?
Spoiler warning: Plot and/or ending details follow.
Jacen's explorations into various Force traditions have often brought him into conflict with more conservative Jedi; not the least of which his own uncle Luke Skywalker. These conflicts can be traced to the beginning of the Yuuzhan Vong war, when Jacen was far less enthusiastic about using the Force for violence than other Jedi. His ordeal with Vergere, however, are seen by many fans as the point at which Jacen diverged from mainstream Jedi thought.
After his five-year sabbatical studying various Force traditions, Jacen is now one of the most powerful Jedi in the galaxy. One of the many abilities he has learned from his time spent with other Force-based societies is the "flow walk" ability which allows him to manipulate time. Among other times, he has used this ability to see through Anakin Skywalker's eyes during the massacre at the Jedi temple. Jacen's new abilities have impressed and concerned the Jedi Masters. Jacen believes that his willingness to embrace different teachings will allow him to accomplish great things (including, ultimately, the galaxy's salvation) while older, hidebound Jedi refuse to open their minds out of fear of the dark side. As of the events of Legacy of the Force: Bloodlines, Jacen considers himself to be the second most-powerful Jedi in the galaxy; he also believes that once he masters Sith teachings, he will be more powerful than Luke.
Canonically, Anakin Skywalker had the most Force potential of any individual who ever lived; it is also a canon fact that Luke Skywalker possesses the same force potential as that of Anakin Skywalker, as stated by George Lucas. Luke Skywalker represents the full power of Anakin Skywalker, had he ever lived to achieve his true potential. In addition, Jacen Solo himself has been the latest in-universe character to state that that his former master is currently the most powerful Jedi in the Order. It is essential to remember, however, that raw potential does not necessarily correlate into actual ability.