Some people prefer one -- some the other. (Depending on what you're doing one might definitely be better than the other for you... for instance, Cubase SX allows 5.1 mixing. Sonar has a fairly robust and developed ACID-like loop functionality that's integrated into the main program. [Actually, CSX just added some kind of loop ability, too.])
Anyhow, it's too important to just listen to a couple of opinions on a BB... you need to check them out yourself, if at all possible.
(PS... I use Sonar 2 and like it very much. But you might prefer Cubase.)
One of my dad's friends turned us onto sonar XL and its GOSU.
We were using vst cubase...but sonar seems to be a bit cooler. I never treid SX so i dunno...but sonar is VAST and i got so many plugins that i dont need anything else. But im a sampler/arranger more then a live recorder...so whatever suits u.
its hot for remixing cuz of the beat matching and all the drum kits and stuff....very very hot...