I consistently recommend a lens when asked this sort of question which is different from the usual. I use one as my "walk around" lens and am extremely happy with it. The lens covers 18-270mm which is too wide to be able to do as well as lower range zooms of equal price BUT it's performance is superb given its flexibility and general capabilities.
It's the (take deep breath) Tamron AF 18-270mm f/3.5-6.3 Di II VC LD Aspherical (IF) MACRO (or some variant thereof). (Mine is the 18-250mm earlier Sony badged, Tamron-manufactured equivalent)
Approximate competitors include.
Canon EF-S 18-200mm F3.5-5.6 IS,
Nikon 18-200mm f/3.5-5.6G IF-ED AF-S VR DX, and
Sigma 18-200mm F3.5-6.3 DC OS,
This lens represents a substantial jump in optical performance compared to earlier wide range zooms - their desultory performance making people think that all "superzooms" must be equally bad. Here are 56 user reviews on the Sony 18-250mm which is the Tamron lens with Sony badges plus faster AF gear ratio plus more rounded aperture petals. 56 users on average rate it (out of 5)
4.29 Overall (4.38 excluding distortion)
Distortion is partially a consequence of the vast zoom range, relates mainly to overall image shape (see reviews) and is largely correctable by various software modules (and is in most cases 'acceptable enough' as is).
The f/3.5-6.3 is "slow" compared to eg a constant f/2.8 that you'd love to own BUT not appreciably different from the f/4-f/5.6 lenses that you mentioned.
DPReview are, in my opinion, amongst the most demanding of review sites. Some may disagree but many agree with this - in my experience, if a product has a weakness, falls short in any measurable way or just "isn't right" for whatever reason, they'll tell you. I've heard claims in recent years of partisan behaviour on their part but so far I'm happy with their reviews (fwiw).
Their review of the Tamron 18-270 is here ](http://www.dpreview.com/lensreviews/tamron_18-270_3p5-6p3_vc_n15)
They by no means give it a glowing report in every aspect. They make it clear that it makes compromises due to the ultra wide zoom range, and they note that it's AF speed is poor if you concentrate on moving subjects. But, given how 'hard' they are on anything they test, this represents a very good result.
- These minor niggles aside, we were overall quite impressed by the Tamron 18-270mm. Where it's good, it's actually very good indeed, and even where it's weak it's not too far behind the competition. And that remarkable zoom range is a draw in itself; this is a lens which will have you shooting the same subject from the same position at both 18mm and 270mm, just to see how it looks. If you often find yourself shooting things which move then this may not be the ideal choice, but if you're willing to put up with its somewhat sluggish focusing it's a remarkably rewarding lens for the money.
I own the older 18-250mm Sony version of this lens.
While I agree that faster or even much faster AF would be nice, it's far better than many older lenses that I've used and is very usable in action situations as long as you are prepared to work harder than you'd do with a crisper focusing AF lens.
For a "universal lens" you'll be unlikely to ever regret buying it. When you can afford to buy a constant f/2.8 do so. Until then you'll enjoy this. 18-270mm on a DX body = 27-405mm! equivalent. My 18-250mm is f/4.5 or less up to about 70mm. That's 1.3 stops worse than a constant f/2.8
Useful re3view and comparisons here
Brief but useful user discussion