I've only used Cubase LE and Sonar 5PE, but what I'll say is this - but it for the features. Sonar seems to have more cutting-edge, universally applicable features, whereas Cubase seemds to do a better job with hardware integration. I was initially disappointed with Sonar 5PE because I bought it, in large part, for the V-Vocal editing, which had problems with phasing. However, they fixed it, so now I'm happy.

The one thing I will mention is that, depending on your soundcard, Cubase may work better with it - for instance, I have an RME digiface, and Cubase allows ASIO direct monitoring, which is just slightly easier than how I do monitoring with Sonar.
Bottom line... yeah, try both of them, compare the features, price, etc... both are great pieces of software.