I think they play slightly different rolls with their sniping aspects. But in general, Northstar isn't as useful. She is very good in team fights because she can snipe more often than ion, does more damage, break shields (which Ion cannot) and her cluster mission is decent aoe damage as long as you place it correctly. Also, Ion's laser suffers from dropoff; once it exceeds a distance, it dissipates, whereas northstar's projectiles don't. Other than that, Ion is probably more useful: her laser shot is much better at killing pilots, and is generally easier to hit with due to no travel time. It also requires no charge up, just the animation to pull it out, and 2 can be fired back to back. However, doing so leaves you with no options so it should only be done if you know you'll be safe or have cover. And if you choose not to devote yourself to sniping you have the splitter rifle and the vortex shield which are decent assault/cqb tools, which northstar has none of. Personally, I think Ion is better more of the time, but Northstar is better in fights where you can constantly see the enemy and have teammates that have their attention. She is also lighter and can thus get around quicker. Her flight core isn't that great, however if you have viper thrusters and you use it off a dash you go really fast, which is great for chasing or being prepared to help a teammate. Otherwise just use it from your sniping position in teamfights if the enemy doesn't have much cover from you. TL;DR: Northstar is a better teamfight sniper. Ion is better overall.