Wow, I didn't even know that braviary was NU! Both are vastly different so it's kind of hard to choose, but I'd choose braviary over swanna in battling. Both birds have few weaknesses which is a great thing. Swanna is effected by thunder 4X and by rock 2x. On the otherh and, braviary is affected by rock, electric and ice moves 2x. The reasons I prefer braviary over swanna is because braviary has a monstrous attack base of 123 which becomes extremely helpful in battles. Swanna is more powerful in special attacks and speed. I prefer braviary because choice band with superpower or brave bird can take two or three pokemon out on a team. Or you can add choice scarf to outspeed most NU pokemon. I also use braviry with bulk up to take out walls and to keep in longer. It's hard to compare the two because I use swanna more for rain NU teams. Swanna is a weaker attacker than braviary, that why I prefer braviary more. Nevertheless, brave bird provided up by roost can become an annoyance to teams as well. I prefer braviary over swanna competitively. I thought braviary was in OU class, shows how powerful it really can be!
In game I didn't use either. I'd probably choose a braviary over swanna for my adventure. With its strong attack strength, superpower and air slash would be extremely helpful in defeating powerful pokemon such as hydreigon. Brave bird would be helpful too but theat move is not unlocked yntil level 63 so I don't know if I'd be using braviary by then. As design, I like swanna's feminine, sleek design over braviary's rigid-aggressive design. Girl swanna probably make all of the boys go wild. :p
To beat swanna, I would simply use choice band with brave bird or return. That would probbaly 2KO swanna. Vice versa, if I used swanna on braviary I would probably euip swanna with a life orb and use ice beam against braviary sincei ce beam would be super effective. If swanna wasn't euiped with ice beam then I would probably use either surf or brave bird instead.