Nightwing - Trained by Batman himself and even was Batman at one point. Proficient in over 10 different martial arts. Tactical fighter. Trained acrobat (more agile and flexible than Batman himself). Good at stealth and a has a lot of gadgets at his disposal.
Winter Soldier - has peak human strength, speed, stamina, and durability in the comics (although the movies have made him superhuman). Expert at hand to hand combat and skilled in the use of military weapons. Has a metal arm which grants him superhuman strength and lets him discharge bolts of electricity. One of the most dangerous assassins in history.
I personally think this would be a good fight but Nightwing would win :P
- Winter Soldier
Most Helpful Guy
In terms of pure fighting ability, Nightwing beats Winter Soldier, but Winter Soldier is a very GOOD hand to hand combatant, who also has a bionic arm and, like Nightwing, is also packing some serious heat.
The main difference between them is that Nightwing does not kill, but Winter Soldier has no qualms about that. Also keep in mind that Winter Soldier uses guns. Yes, Nightwing knows his way around guns, from simple thugs pulling small pistols out, to well trained mercenary guards, but this is one of the deadliest soldiers/assassins in U. S/Russian history we are talking about here. Put a simple gun in the hands of the right person (ex. Deadshot, etc), and a gun turns from a simple laughable henchman-wielding pea shooter, to something actually very deadly.
I like Nightwing better as a character, but if the chips were down and this was a fight to the death, Nightwing would lose in my opinion.