I have owned both fairly equal amounts of Steelseries and Razer products and I conclude Razer suit 'me' more.
The reason why I prefer Razer is simply I have been using them since the Razer Boomslang days, and they have always offered products that suit my type of grip and aim style in games, and I have had far less problems from the start. Steelseries on the other hand, I have been through 3 of their mice and each one had major tracking problems and I wasn't particularly keen on the grip shape of them either:
Kinzu - tracking and acceleration problems
Ikari Laser - tracking and acceleration problems plus problems with certain surfaces
Ikari Optical - tracking and acceleration problems
Steelseries support kept saying it was a driver problem and it would eventually get fixed but it never did. Lots and lots of people had tracking and acceleration problems with these mice. I don't know how they fair now however as it has been years since I have last looked and it is possibly they may have fixed the problem eventually as many believed it was a hardware fault. Certainly though when the Kinzu and Ikari first came out, there were lots of problems - I know because I searched tirelessly across the net and saw many other gamers complaining on various forums. Not only that, Steelseries themselves admitted they were 'aware' of the problems.
When compared to the Razer products I have owned:
Razer Boomslang - perfect for all my use but mouse died eventually after a few good years use
Razer Diamondback - perfect in everything I played but left click stopped working after 2yrs
Razer Copperhead - the best of the bunch so far (really loved that mouse) but sensor and mouse wheel died after 4 or so years.
Now I am using the Razer Imperator 2012, and although I don't think it is as good as the Copperhead, it serves my needs perfectly and the build quality is the best I have seen yet from Razer, or any mouse for that matter - I have owned a fair share of Logitech and Microsoft mice as well to compare to.
I won't knock Steelseries though, as they do make good products its just I don't like their mice, and 3 bad experiences with 3 different mice left me feeling bitter. They do make excellent mouse pads though, and I have been using their mousepads and nothing else for years, and they also make good gaming headsets as well.
