Whats better in ear or on ear headphones?!

I don't think Beats headphones have noise isolation, otherwise I would recommend the over-the-ear variant.

For optimal audio, I say go with the in-ear. They allow quieter play in louder environments and in general offer a more "stable" experience because of it. Conversely, they also have smaller drivers and the over-the-ear variant may provide more powerful audio, particularly for bass.

For optimal comfort, go with your gut because some size ears are going to better appreciate one or the other. If you're highly active, you'll probably want in-ear headphones lest you literally bounce them off of your head; this also applies if you have the habit of headbanging a lot.

Personally, I would go with the over-the-ear at this time for the convenience of hanging them from the neck (I can't tell you how many times I've stepped on my IEs), they need less cleaning (ear wax IS disgusting!!!), they're more flashy (love that rocker style!), and I'm pretty sure they save your ears.

I myself am something of a couch potato, so I'll be purchasing the Logitech G35 gaming headset. Noise cancelling, surround sound for games and movies, and I hear they have AMAZING sound, but at the same time, they're USB so I'll also be getting a pair of buds for my MP3 player.

All in all, it's your choice. Try them both on, I've seen a few places you can. Staples and Radioshack, maybe Walmart. You should be able to jack your MP3 player right in right there, just give those buds a nice wipe with your shirt; I don't trust other peoples' ears.

EDIT: First-aid wise? I'd go with over-the-ear hands down every time. Canalphones are murder at high volumes and I myself wind up fuzzy with my V-MODA Vibes if I'm not careful. At the same time, they'll be AMAZING if you work in a loud environment. Less juice for more battery AND they double as earplugs!

I have the in-ear ones and I'm about to return them for the on-ear ones. They were uncomfortable and I had to sit still otherwise they'd come out.