Thats a hard one, lookswise, i think they're both pretty cool on the exterior, BUT i've always had more trust torwards a chevy than a ford for some reason. I would say the chevy.
I had a 01 f150 supercrew lariat. If you're gonna buy the Ford make sure to get the 5.4L, a few more horses and better for towing. In 03 they came with a sunroof on the supercrew too. I have only test drove the GMC models so I cant comment on those. Im in the same dilemma as you. The Titan my girlfiends Dad has is sick though and great to drive!