I've been going through the same comparison myself, in the shops I've found the following comparisons:
Samsung Pro's:
Gutsier, brighter picture, sharper. Many picture adjustable controls.
Blacks are deeper. More contrast. Picture looks "polished".
Samsung negatives:
Shinier screen attacts more reflections.
Off axis viewing poorer.
Couldn't eradicate that white lcd highlight clip you get on peak whites. Hightlights Looks "burnt out".
Pixellation on movement more evident.
Panasonic Pros:
Off axis viewing excellent
Matt screen has virtually no reflections
Picture is "crt like " ie picture looks solid with no highlight clipping on peak whites.Skin tones look more natural
Picture easy on the eye, not oversharp
Screen sits lower on the plinth, does not look too big in a small room.
Styling looks less offensive, Samsung looks a bit tacky with that perspex strip at the bottom in my opinion.
Panasonic negatives
Picture looks slightly duller, softer and greyer
Blacks are not as deep.
Screen contrast has to be up 90% or 100% to get enought brightness.
Only basic picture and sound adjustments, but responds well to increasing sharpness level and going from Dynamic to normal, and cool white balance to normal.
Preset adjustments look good in my opinion, and don't need too much tweaking to get a good picture.
Whilst the Samsung has a sharper, bolder picture I feel the Panasonic looks more natural, and avoids more of the LCD artefacts than the Samsung