The IM50 has much fuller mids - I don't think of the QB2 as V-shaped, but they sounded like it when I switched from the IM50 earlier today. They both have good soundstages, with the IM50 a bit more immersive and 3D. The IM50 are built very solidly, though I don't know how reliable the cable connectors are yet. They're also quite big and bulky; any more so and they'd be too uncomfortable for me. The LG are smaller and lighter, and mostly disappear in your ears, while the AT stick out a bit (and the memory wire may be annoying to some). I'd say the IM50 are better in most ways, though if you like pronounced treble sparkle you might find them a bit tame up top. The QB2 have more sparkle, but still stay smooth, plus they have the headset functionality (including volume controls, which not many Android headsets have). They're both bargains.
Thanks! You aren't making this a lot easier though. :D The sound signature of the IM50 might be better for me than the QB2, though I really quite like these as well (at least as far as sound goes, I'm not a big fan of their comfort, or lack thereof). How's the bass of the IM50 comparatively? Ideally, I'd be looking for a bit less midbass and a bit more subbass, but I don't really expect the latter here.