I was in the same boat, I was sure I wanted a Panny, viewed many and read reviews, it seemed the Panny got worse with age while the LG got better.
My 590 is pretty good, in my opinion it is better than the Panny, I have no problems with blacks and the image has only improved since I bought it. Image retention was noticeable but seems less of an issue as the screen gets used, logo's that did give image retention don't seem to affect the screen now, my kids watch Cartoon Network and it used to be visible when I got home, these days there is no retention of the CN logo so I can only assume it is due to the screen improving with age.
I never had any buzzing with my set when new, but these days at around 6am 7am or when it is pretty quiet, during bright scenes if the volume is off a slight buzz can be heard from a metre or two away here.
I should add that it is THX certified and pretty much out of the box when set on THX mode it is bang on, I reduced some settings due to it being recommended while it got it's first 200h use, but that quickly got forgot, it is on all the time (family) and THX seemed to be the family preference, not done any tweaking updating or screen whitewash, bought the 590 over it's cheaper sibling simply for the THX certification.
I got mine for £770 with a five year guarantee and two free QED HDMI cables. My only regret is not waiting for the 60" instead.