wanger, they are both pretty good sets. What are you wanting to use as sources for this thing? That could to have strong relevance concerning your decision.
I tend to favor the Sony S3000 over the Samsung 53. But the 53 looks nice....Samsung has a history of HDMI troubles it seems like though. The GV42LF is getting good quality control feedback, lots of problem free sets. The 42 inch Vizios are generally considered to be the best of the Vizios as far as PQ is concerned, as well.
I own the GV42LF and I love it, very impressed by its performance and features.
If this is your first flat panel HDTV, you will probably be thrilled with either one.
Epson 8350 / Panasonic AX-200u / Optoma Graywolf 92" / Draper Luma 92"
Samsung 51F8500 / Panasonic P50ST60 / Vizio P502ui-B1 / Sony 50W700B LCD
Sony S790 / Panasonic BDT-220 / Roku 2 XS & Roku 2
Samsung F550 / Speakercraft CS3 / Yamaha YAS-105