I use a Razer Kraken, and it is my first real gaming headset. It works very well and I'm 100% satisfied with my purchase. It is noise cancelling with helps with immersion and concentration, it has good audio and a nice flexible mic and overall it's a good quality headset for the price. The only problem I had with the Kraken was getting used to it, since it seemed heavy at first and was probably due to the fact that I wasn't used to a more sturdy, quality headset. Though after a couple days I got used to it and I've been using it for 6+ months with no problems, and now of course enjoying it a lot.
I'm not familiar with the Tiamat, so I can't speak up about how well it compares to the Kraken. If the reviews are better overall, it is likely a little nicer. It is $20 more, which probably accounts for a slight increase in quality. It probably will come down to how much you are wanting to spend and which looks cooler to you. I think you'd like either headset though, Razer has really great quality peripherals.