Hey cooperman,
Personally I would try to mix to speakers, because that's what people are going to hear you on.
I know I'm going to catch hell for this, but Radio Shack sells koss phones, with their name on it.
I have a pair of sonys, and side by side the Koss are much more efficient, and don,t sound as muddy. I think they give you a better depiction of what's going on sound wise. The Koss are also much cheaper. Good sound is where you find it!!