Hi christie:
I have an Omega 180 and I love it. The optics are great, it is lightweight, and fits really well. Most of my class either got the Omega 180 or the Keeler Vantage. I tried on the Omega 150 and it fits fine also, I just didn't like how the filters needed to be attached and are not included on the headset.
I didn't go for the Keeler Vantage because although it is wireless, I'm not that comfortable having a battery pack near my brain. =) Maybe I'm just being too paranoid though. Also, I don't think the Vantage comes with a small pupil feature and it was important for our clinic professors that we become really good at small pupil BIO.
Heine came out with a really nice soft backpack for their BIO last year, also! The difference in price between the 150 and 180 was only $154 through the reps, so I went with the slightly higher priced 180 (I think it's a good investment).
Best wishes,
Rosanna