I'm a dual-owner of GW and DW and I find useful and enjoyable bits in both product lines. If I had to make a choice between the two I'd go with DW for a few reasons.
• GW seemed to hit End of Life simultaneous with its release. DW, on the other hand, is ALIVE with regular doses of errata, free enhancements, and new material.
• GW content feels uneven. I understand the need and especially the desire to take submissions from many talented sources, but there are many crunchy-bit areas that appear to have escaped the editor's smoothing-out influence. DW feels internally consist and competently edited.
• GW has (at best) a lackluster web presence. The Sword & Sorcery web site is clunky and their forums, well, their forums suck. Bad. Whatsmore, the GW-specific pages were orphaned even before the second book in the product line was released. In contrast, the RPG Objects site friggin rules! I purchased the DW PDFs through rpgnow, created an account on the RPG Objects site after some gentle prodding, and am now informed when updates (a.k.a. FREEBIES) are made available.
So, yeah. Good stuff from both camps, but DW wins the cage match.