Your best bet is to read the forums at www.avforums.com (UK) or www.avsforums.com (US), they have some very knowledgeable people on all matters regarding TVs and home theatres. You’ll get reviews of pretty much every possible component, alongside listings of all the faults of a particular bit of kit (which is useful if you’re comparing two options and need to decide between them).
In dark and/or action scenes I see some blockiness even on pure 720p and 1080i ATSC antenna channels, which is going to pretty much be best case quality. It’s a compression artifact, hopefully compression techniques will get better over time.