Gordon did a wonderful review of the EF-S 18-200mm
I would recommend watching the video review of that lens at the very least.
Another option would be a Tamron 18-270mm as it has a longer range.
If you only want a single lens solution, that is what these lenses are designed for.
The trade off for the versatility/compactness/price is image quality, but that would occur for any super zoom you buy.
These are not bad lenses. They are absolutely fantastic for what they are intended for; which is a muti-purpose single-lens solution.
One thing you could do is rent a copy of the lens for a bit to see if that would work for you.