Are we counting Taskmaster;'s second mini-series? I remember in that one he was able to unload all of his techniques in one combo. Whether he takes it or not, in my opinion, is if he already has all of his former copied skills and his sword, shield, and bow. With these three weapons he can duplicate the greatest marksman in the Marvel Universe and Captain America, who pulled a draw against Batman in an earlier battle and even bested him in the crossover comic. In the end I think Taskmaster can take the fight.
I think Arrow can take this fight. since it starts at about fifty feet he can easily utilize his various archery skills to keep Widow at a distance. Even though She can pin him similarly with her pistols he has been shown able to defeat several opponents armed with automatic weapons as well as the skills of Deadshot even with his wrist mounted automatic pistols, taking a shot from around a pillar long enough to put one through the assassin's eye.
In hand to hand I have seen Widows very advanced skills, though Arrow is able to hold his own in that respect. He has defeated several men in closed quarters simultaneously and engaged and defeated assassin China White in single combat. He also received training from Slade Wilson during his time on the island. While he may not be on Black Widows level in that respect he is more prepared for this type of situation than Hawkeye. If Natasha does get in close I think it would be an even fight.
@compac: Definitely need to give Nightwing a show. DC seems to do a poor job of highlighting any characters that aren't Superman of the Batman. They have tons of characters that have potential. But yeah, i'd watch a show about Dick Grayson. Also why can't they just make DC Nation a two hour slot, that way they don't have to cancel shows just to put new ones on?