It really is a tough choice between these two units here, because each has features that I would like to see in the other one.
If SteelSeries put in some more responsive driver units to deal with the volume issues, then they would be my firm recommendation.
The Razer Piranha on the other hand overcome the volume issue by going with a different style of ear pad sitting directly on the ear itself. However, it is unfortunate that this can lead to the dreaded head pinch and ear burn with extended use. Furthermore, the microphone placement is an issue; it would be nicer to have a bit more flex and stay with it to ensure you can get it near the mouth.
Now, here is what it can mean for you. If you are a hardcore gamer who spends lots of time with the cans on your head, I would have to say go with the SteelSeries. The sheer practicality of these units means that you can wear them comfortably for hours on end, and they give a great range of delivery so you won't miss a cuss.
If you are more of a casual gamer or you just like the shiny blue things (I fall into this category), then the Razer is more for you. Don't get me wrong, the Piranha is still an excellent gaming headset, but it suffers from two major stopping points that can mean the difference between a few hours on COD4 and an all night marathon. The head pinch factor can leave you a bit sore after a few hours and the units' inability to pack down into a smaller size can lead to breakage when packed in with the rest of your gear.
The conclusion is that both units will give you superb auditory performance and both are solid brand names that are reliably pumping out one solid product after another. The choice really comes down to your preference and style.
SteelSeries 5H v2