I want to go with Nikon because I currently have a Canon Rebel EOS and it's about 7 years old. I paid almost $1,000 for it and it has NEVER taken good, crisp pictures. I have experimented with the settings a lot and nothing really helped. Now, the pictures are okay, but I'd call them P&S quality. My daughter's Kodak Easyshare takes better pictures. A couple years ago a woman approached me when she saw me with the camera and told me she had the same problem with hers. She had replaced a Nikon P&S and was thinking of just going back to that.
While I won't try to dissuade you from moving to the Nikon camp (I'm a big Nikon fan), your lack of sharp pictures is probably due to the cheap glass on the front of your body.
You can have a brand new top of the line $7000 flagship body, if you put a cheap piece of glass on it, it's going to make it look like a cheap camera. Conversely, you can get an entry level D3100, slap a good piece of pro optics on it (12-24 2.8, 24-70 2.8, 70-200 2.8 in Nikkor zooms) and take spectacular pictures. This is why I've generally stuck with prosumer/enthusiast bodies instead of flagship pro bodies, I put the cash I saved towards better glass. Most of us don't need 9fps and the massive buffers you get with pro bodies. Hell, I've shot an old D100 for a long, long time (a circa 2002 body mind you), only recently upgrading. And honestly, the only reason I'm upgrading is for a new, better sensitivity sensor, not much else. The other thing my D100 has really restricted me on is shooting high ISO in low light. Don't get me wrong, I've spent a lot of time behind the newer bodies over the years and had the lust to upgrade, but I just ended up spending the coin on new glass, carbon fiber tripods, better accessories, etc.
Honestly, bodies are pretty much almost disposable these days, unlike film bodies. I paid $2000 for my D100 8.5 years ago, I'll be lucky to get $200 back out of it. I'll get over twice that for my 13 year old Nikon F5.. I'm getting way off topic here.
You can't go wrong with Nikon or Canon, both make great equipment. There are popular focal lengths in each system, similar pricing and similar quality. Canon does some lenses better than Nikon and Nikon does some better than Canon. In "pro" glass, they're both top notch.
Do yourself a big favor, don't factor that piece of glass you currently have into what system you're going to shoot. Get rid of it, it's on the low end of bad. Then go out to your local camera stores and see what they seem to stock more of and see what FEELS more comfortable to you. The Canon 60D and 7D are both great bodies that rank right up there (again, pros and cons to both systems) with the Nikon D7000 that I picked up, but I just can't get used to the Canon ergonomics, it's just not comfortable for my hands, I'm simply a Nikon guy, I'm used to their ergonomics.
See what ones feel the most comfortable, then pick from there. Does your local shop not carry Canon very heavily or not at all? Ritz Camera has stopped carrying Canon almost entirely at this point, for example. And if your area is like mine, Ritz is the only "decent" camera store around. We have exactly one "real", non chain camera shop in Pittsburgh and they are TERRIBLE. So for me, it's Ritz or mail\web order. Maybe factor that into your decision. Do they favor Canon over Nikon, then again, factor that in.
But regardless, put some decent glass on the end of it. I see many new SLR users that just can't stand the idea of putting a piece of glass on their camera that costs more than the camera itself does, but I assure you, this is the right way to go!
Oh, and don't necessarily get caught up in the megapixel wars. Anything over 10 and you're fine as long as you compose the shot decently and don't have to crop the hell out of it. My 6mp D100 has produced many 8x10's that look fantastic.
HTH
