It's not Cubase that doesn't sound good on your system, it's the way your system is tweaked or not tweaked and/or your I/O. Sorry to be blunt. There's very little sonic difference between Cubase and Samplitude in the hands of the right engineer.
That said, I'm really a fan of the Cubase GUI. I'm not a fan of the company, though it's present alliance with Yamaha is starting to thaw out its relationship with its users somewhat (you now have communicators like Yammy's George Hamilton who has done so much on this forum in his N12
thread). GUIs are important, because if you don't like kooking at the program 12 hours a day, you might not feel like going that last little bit that gets you to greatness.
Samplitude's strengths are many. The fact it has built-in CD burning and all kinds of effects is a real plus. Sam developers are a billion times more communicative than Steinberg developers. Unfortunately, I'm really not a fan of the program's look and feel even with skins. The MIDI is definitely improving all the time. Samplitude is just really strong. I wish it lured me in more visually.
Those are the two I'm most familiar with. I use a combination of both.
Reaper is way cool in certain respects but owner Justin prioritizes sound over visuals - that's a fact, not a criticism. For price and sound it's awesome. I personally couldn't work with it, but I'm not you.
I am finally hearing good things about M Powered (Pro Tools) 7.4 for Windows. I'm going to give that a thorough workout, because I like myself as a tracking engineer, not as a mixing engineer. Most of the engineers I'd want to do final mixes for me have Pro Tools systems - the files are transferable directly. The MIDI is supposed to be actually good now which has never previously been the case. The downer might be that TDM plugins cost more than their VST counterparts.