Is the Canon 18-200mm EF lens considered versatile?

I own a Nikon D3100, and two lens: the 18x55mm VR and the zoom 55-300mm VR both from Nikkor (Nikon). I use it almost daily, and I realize that for my uses, I find myself needing to switch from indoors (I use the 18-55mm for this one) to outdoors (55-300mm). I find it a hassle to keep switching out these lenses almost every time I use them, and I usually carry my DSLR and my 2 lens w/ me. These get heavy after a while, so I'm considering a compromise between the two of these lenses that A.) meets the ranges of the focal lengths between the two and B.) that I can use only one lens instead of bringing two. And also, I'm planning on getting a Canon 60D or Rebel T3i as my next DSLR purchase in the near future, so I'm buying lenses that will fit those (as per the Canon 18-200mm EF lens). I'm aware that I need to get an additional mount adapter to use the Canon lens on the F-mount of my Nikon.

So what I'm asking is this: Can the Canon 18-200mm lens do everything (and more) than my Nikkor 18-55mm? I heard about the focus of the 18-200mm is considerably wide, although (b/c I'm new to photography) I'm not sure what that would mean.

And if I do get the Canon lens, I might consider selling my 18-55mm depending on how good the Canon lens is. Anyway, any input would be appreciated. Thanks!

Added (1). I'm thinking about upgrading to a Canon 60D or a 5D Mk II in the near future, but that's not until after 5 years.

Added (2). I might buy this lens used (if I decide to buy them at all)

Okay, why do you want to get the 60D or T3i in the future? You already have a Nikon system. Unless there's something you absolutely need on those two cameras, it is useless, and actually kinda dumb to change

Next, you do realize that Nikon has it's own 18-200mm lens, right?
http://www.bhphotovideo.com/...200mm.html

as to actually answer your questions, yes. The 18-200mm lens is considered versatile and basically replaces both the 18-55 and 55-200, but by no means specializes in any one area of lenses.

It means

A. Its hard to manually focus because you have to turn it more.
B. The 18-200 would have a TERRIBLY slow autofocus. So anything moving would be hard to get.

i assume you have a 18-55mm f3.5-5.6 right? Standard kit? Make sure your 18-55 has a wide f stop like f/2.8 or at least f/3.5. The wider the appeture, the more expensive it will be. Some lenes may have a range. Like an f/4-f/5.6. Thats OK, but its not the best.remember, a larger f stop will do better in low light photography and will give you that nice blurry background for close up photography.

its always good to keep your nikkorr 18-55 standard kit, although once you have your broad spectrum lense, you might not use it. If you don't use it that much after a year, you can sell your 18-55 and maybe your d3100 and save up for a 60D (i highly recommend stepping up to the canon eos 7D or 5Dmkii if you Really are into photography or you start feeling you need more image quality because your going proffessional)

18-200mm lenses have nice versatility, but there's some sacrifice in image quality. You might be able to reduce your lens changing considerably by getting the 18-105, which is reputed to have more consistent image quality. If you do want 18-200mm then get the Nikon lens. It costs twice as much as the Canon, but it is better quality.

Have you considered getting a Tamron 18-270mm lens for your D3100 so you won't have to jump ship and save on dollars? That would almost reach the range of your current lenses. Beware though. Zoom lenses aren't the best in the dSLR world, the longer they zoom, the poorer the optics become. It doesn't matter what brand you are in, the rule is the same.

Swapping around two lenses really isn't a hassle. I survive though with just one manual 50mm prime lens most of the time.

You have a perfectly fine camera. If you want to upgrade, look at the Nikon D7000.

Here is how the D7000 sensor compares to the Canon 60D

http://www.dxomark.com/...nd2)/Nikon

As you see, when you compare cameras at the same technical or user level, you get a better idea of how they perform.

Compare the Nikon D3100 to the Canon T1i/500D
Compare the Nikon D5100 to the Canon T3i/600D
Compare the Nikon D7000 to the Canon 60D

Comparing oranges to oranges is the only way to determine which camera performs the best

Here is how the full frame Canon 5D, Mark II and the full frame Nikon D700 compare

http://www.dxomark.com/...nd2)/Nikon

As you see, the Nikon with only a 12 mp sensor out performs the 5D, Mark II with 21 mp especially in low light situations.