I've tested 2 out of those 3 models (razer tiamat and akg 701), and both were fantastic headset, but they're tailored towards two different markets. The Razer tiamat is specifically for gaming, while the akg 701 are meant to be an all-around headset for music, movies, etc.
It really depends what your primary use will be. If it's gaming, go for the razer tiamat; it has excellent directional audio and an external control unit that lets you switch between audio setups on the fly. See the review
If you're more concerned with music and general audio, than go with the akg 701s - they have a huge soundstage so they'll pick up a lot more in music scores - especially classicals - but won't stand out in gaming though.
best of luck!