obviously it's a matter of preference, but i quite like the last row of PE for the guilt free recline
i've never experienced noise from the cabin behind, any noise has come from the front of PE or from UC!
you'll be last served though, so a popular meal choice may be gone by the time the trolley reaches you
connecting at ATL seemed quite smooth, the immigration hall has good capacity, if you've previously entered USA at least once before on ESTA you can use the kiosks there
after that, you get your bags from the carousel and go through customs, then you come to the transfer area, on the left is the belt to drop your bags if they are already tagged for final destination, otherwise there are airline desks on the right
i went through there in january, VS LHR-ATL, DL ATL-MCO, the VS flight landed late, i was one of the first to get my bag and drop it at the transfer belt, but my bag still didn't make it onto my DL flight, others on the same and later DL flights were missing their bags too (the MCO baggage help office was being kept busy!), DL could not say where my bag was, their systems claimed it was still on the ATL carousel!
the DL lady said the TSA sometimes cause delays screening bags, which could be why it was not yet showing in DL's tracking system
she took my details and gave me a link to the
http://wheresmysuitcase.com/ system that they use, i added my email etc. to my record and over time it sent me updates as things happened, my bag eventually was delivered to my hotel about 0400
you'll probably be fine, but if your connection time at ATL is less than 3 hours i'd play safe and put overnight essentials in cabin baggage (including phone/laptop chargers and plug adaptor!)
once you've put your bags on the transfer belt, you go through cabin bag x-ray and security check, then head for the train to the terminal for your onward flight - there are several terminals, you need to check which one before going to the train, i almost missed this vital step!
for duty free, the TSA says you can now take liquids in cabin baggage through transfer as long as they are in a tamper evident bag, but the duty free shop at LHR claimed this was not true - so you may have to insist on them putting things in a TEB (otherwise you will not be allowed to take them through, and it will be too late to put them in hold baggage)
on return, once you are in the ATL international terminal there're restaurants upstairs, the italian one was quite good, there's also a DL lounge you can use if you are VS AU, but it's nothing special and was quite crowded when i was there, not sure i'd bother going in again