R400 any time of the day. Better performance, more solid, a bit spacier than the R300. Easier to assemble.
On a side note: I am a bit biased though, because for me a side window is a minus. Also the R400 reminds me a bit of my favorite Cooler Master designs.
Yea, cause the more I think bout it, its gonna be right against my desk side, so I wont be really able to see it too much, so yeah, I'll probably be getting 400r