I bought 3 TVs this week and can offer the following opinion:
At 50" I think the Pioneer FHD-1 plasma is going to offer you the best picture for anything but gaming and PC use. It can be found for around $6,200
If you want an LCD look at the new Sharp D62 52" ($4,200) and the Sony XBR2/3 52" ($6,400) for the best picture.
At 57" you might want to check out the Samsung.
I just purchased a 37" Sharp 37D9U (1080P), a 32" Sony KDL-V32XBR2, and the brand spanking new Panasonic 65" 1080 commercial plasma, the TH-65PF9UK