So, anything with 31" and greater weapons that can shoot on the move that are not str 4 and under would be good in a 1 on 1 duel with NB on a REALLY big table.
In smaller tables, where you'll eventually get cornered, turbo-boost is good then
So:
>30" Gun
>Str 4
Assault weapons (for foot soldiers)
Turbo-boost special rule.
We have destroyers, heavy destroyers, SM Landspeeders (hvy bolter, missile system), SM Bikers with the Assault Bike (hvy bolter), Eldar Falcon, ELdar Fire Prism, Eldar Vypers, D. Eldar Ravager, D. Eldar Raiders.
Things that don't 'tubro-boost' that apply to the rest of the options:
Tau HammerHead, Tyranid VenomCannon, Any Eldar unit that carries an EML, BL, SL, Dark Eldar would have the dark lance. IG, SM, and Chaos have their plethora of weapons.
Really, NB's weakness is snipers, poison, rending, being 360 points, and phase out. So in a 1 on 1 duel, with 0 necrons on the table, he'd phase out, ... but that be wishing for too much in a "friendly" character duel...