Worst:
Marth, Toon Link, and GaW.
I haven't played a good GaW yet, but from looking at the character's potential (bair) he ***** everybody.
I also have yet to play a really spammy toon link but that's the problem. He's the only character (besides Link) where Ness can't do anything to their projectiles except dodge, shield, and bat reflect (situational).
Marth is still a problem, but nowhere near as bad as in melee.
Pit probably will cause problems until people learn that Pit has one of the most gimpable up-bs ever. Then the pit players will learn how to glide, then everyone learns to edgeguard that. I just spam fair and make good use of the psi magnet cancel.
Link could cause problems if u have a hard time approaching him. Watch of for that dair.
Unlike other characters he doesn't have a matchup equivalent to his sheik matchup in melee.
Use psi magnet to push away snakes grenades. Use pk fire to blow up his d-smash bomb after he's planted it and he's still close to it.
Ness' fair is still good, SPAM it. Upsmash is good too ^_^. D-smash is like a reverse up-smash or w/e lol.
IMO: Ness isn't top tier material, but he certainly isn't trash. He's still underrepped by good players (like in 64 T_T). I predict him to be mid tier most likely. At best lower upper tier. I can't see him being low tier as he really doesn't have that many bad matchups compared to a lot of the characters (Mario, PT, Samus).
As long as a counter to him equivalent to shiek in melee doesn't happen, he's playable in tournaments IMO.
Edit: He won two times who won two times? I think Ille qui vincit bis, vincit bis works better?
Da mihi caput =P