I don't battle NU much, but competitively I prefer Beheeyem over Swoobat. First of all, swoobat is a lot easier to take out than beeheyem because swoobat has more weaknesses (rock, ghost, electric, ice, dark) than beeheyem (bug, ghost, dark). Also, beeheyem is better defensively than swoobat so normally he's in for a longer duration which can help me out more. I also prefer beeheyem over swoobat because he's just done more for me in the NU battling scene. With choice specs, he's a monster becoming one of the strongest attackers on the NU playground. Or you can implement a life orb on him with recover which helps beeheyem. Also, beeheyem is also a good choice for a trick room team - which I haven't used him in- because his speed is so low. Add trick room with nasty plot and beeheyem will rip a team apart. On the other hand, swoobat with CM can be a good sweeper, but I just prefer beeheyem over swoobat. I believe that swoobat will be used in more NU teams that beeheyem just because beeheyem is slower. Swoobat has a special moveset that can also rip apart teams. Swoobat is also easier to implement in a team than beeheyem is.
Personally, I used swoobat throughout my journey in Pokemon Black. I don't believe that I used him when battling the Elite four though. I thought that he was a good Pokemon with good typing, and helped me tremendously in the gyms (especially at the 3rd., 5th. and 6th. gym). I didn't think he would be strong enough when I versed the Elite Four because he got KO'd too easily. Now that I look back, I wish I had caught an Emolga instead. Oh well.
I like the beeheyem design more! I lie the robot look that Gamefreak gave him, and I just like his futuristic design. I could see him in The Jetsons haha. Swoobat's design is cool but a robot is cooler than a bat any day.
I think that swoobat could defeat beeheeyem with its speed. If it was able to CM a turn or two, then hit beeheyem with air slash or HP ground then it could defeat it. I think that beeheyem has more of a chance defeating swoobat though. If beeheyem used thunderbolt or maybe even signal beam against swoobat it would probably result in an OHKO. If beeheyem already had trick room implemented then it would be a no contest outcome on who would win.
Overall, I prefer beeheyem over swoobat. Woo.