Sigma or Canon lens

[the_game22]

I am looking to get a new lens with a fairly wide range of zoom to take with me on vacations. Hopefully this will let me get by with only taking one lens. I was thinking of the 18-200.
Is there any significant differences between the canon lens and the Sigma lens. I am looking to go with the stabalized lens if that matters. If you have any suggestions on any other lenses in that price range that would be good to consider let me know.
btw I am using an XTi, and am fairly new to the DSLR's. I am however still saving up for a 70-200 F2.8 IS for taking pictures of my kids sports.

[Mitsu3000gt]

A main difference between the Sigma and the Canon is that the Sigma is a full stop slower when your zoomed out to 200mm at 6.3 vs. the Canon's f5.6. So, if both lenses are at 200mm, the Canon can let in more light and get you a faster shutter speed if needed.

As for image quality, neither are outstanding, but likely perfectly acceptable for casual shots on a vacation (most people use them for that).

Here are some links to reviews on the Sigma:

http://www.dpreview.com/lensreviews/sigma_18-200_3p5-6p3_os_n15/

http://www.popphoto.com/cameralenses/4603/lens-test-sigma-18-200mm-f35-63-dc-os-af.html

http://www.photozone.de/canon-eos/321-sigma-af-18-200mm-f35-63-dc-os-canon-test-report--review

And the Canon:

http://www.dpreview.com/lensreviews/canon_18-200_3p5-5p6_is_c16/

You could check out the Tamron 18-270 as well, but at over ~$1000 I think its a huge rip off.

[AccentAE86]

There is also the Sigma 18-250 OS if you want extra range, but it's not quite in stock yet if you can wait.