I've been happy with my Panasonic FZ10 -- for long-zoom daylight shots.

But I need a wide-angle (28mm) lower-light (ISO 800+) camera.

I've got three distinct uses for a camera:

My candidates are:

The Canon is the speed king -- in terms of ISO and performance.
The Olympus is weatherproofed and built like a tank.

I decided to try the A2 as an interrim step. This is a comparison of the A2 and FZ10. Quite a lot of this also applies to the FZ15 and FZ20. Note that it's based on 6 months with FZ10, 1 day with A2!

Feature A2 FZ10 And the winner is ...
Zoom Manual

Lever.

Takes 5 seconds for wide-to-tele zoom ... and then focus is slow at high zoom.

A2 is the clear winner. This is the single best feature.
Power Button Slider FZ10 is winner. On A2 can't be sure its on without looking. Can be turned on accidentally in camera bag
Exposure

Mode dial, wheels for A and S

Shows values and histograms, but NOT the exposure value relative to what auto-exposure thinks is right.

Set mode in menu. Press exposure button (after 6 months I still can't find it!) then use menu arrows.

Shows values, histogram and relative exposure value.

A2 is clear winner on everyhing except exposure value.
Auto Focus

Quicker in light, slows down in dark.

Focuses too close ... can't focus through a car window.

Slow at high-zoom. A2 better where it counts, but not perfect.
Manual focus

Direct manual focus after auto succeeds (or fails). Slider from auto to manual (for prefocus).

A2 shows focus distance, and knows where infinity is.

Magnify button is hard to reach, but fills the whole screen, but button is hard to reach.

Spring-loaded 1-shot focus makes it very easy to go from auto to manual for prefocus.

Spin the wheel to the right and it MAY stop at infinity.

You can set the menu so that the central part of the screen is always magnified --- too small an area to be usefule, and too large an area to see the context.

 Both have (dis)advantages.
EVF

A2 is much bigger ... but colors look washed out (actually, they're pretty close to what the eye sees!)

With sun behind, bright reflections of my eye/spectacles. Probably need an eye-cup.

FZ10 is small and bright, with high color contrast. No reflections. When A2 boost came on FZ10 was still clear and bright.
LCD

Swivels in one dimension.

Completely washed out in sunlight.

Fixed, but better in sunlight.

I seem to take a lot of shots with the camera held up and over a fence (bird-watching and construction sites).

Swivelling LCD would be great if I could see it!

Lens

Flare at wide-angle when shooting towards sun, even with lens hood on. EVF was totally washed out by glare, and focus had a problem too,

Extension lenses hang off nose, and (?) can only be used at extrme wide and tele.

Excessive CA after 300mm

Winner for high-zoom. Tele lenses are better, because the sit on a seperate extender, and zoom still works (with vignetting up to 2X).

I'll add a TCON 17 "permanently" to the FZ10 giving me about 200-700mm.

A2 for wide-to-mid, FZ10 for exterme tele.
Dials and Menus. On the whole, for A2 you turn a dial, press a button and roll a wheel.

Menus, except for exposure-related stuff where you use the control arrows.

Easier to toggle burst mode, adjust EV.

 
Lots more stuff

5 Custom settings. Interval timer (except minimum interval is 30 seconds). Raw. Control from PC (extra $). Wireless flash control.

FZ20 has two custom settings. A2 by far.
Overall speed. 2 second start-up, manual zoom, quicker daylight autofocus = MUCH more responsive.

4-second start-up, 4 seconds to zoom, 2 seconds to focus = missed shots!

Feels slow after A2

A2 by far.
Write times

A2 is slower ... I thought it had locked up, but its buffer was full.

That's 8MP Fine jpeg ... 3-4MP files

   
One-handed use. Everything except zoom. Yes, I have been to a barbecue with my FZ10 in one hand and eats in the other.  
Macro Works at a distance. FZ10 focuses at about 1cm ... but who wants creepy crawlies on their lens? ... and they're in the shadow anyway.  
Bottom Line     If you don't need the ultra-zoom the A2 is better.

Pictures ... in most cases cropped.

Feature A2 FZ10 And the winner is ...
Zoom The A2 is noisier, even at ISO64 vs 50 for the FZ10
Focus

A2 locked on immediately.

Had to focus manually with FZ10.

36mm Again, A2 is noisier.
Moon No contest.
ISO 100  

ISO 100

x3 in PSP9