Has anyone used both ? Which do you prefer ?
It depends on the printer you're using and the look you're going for. I've used both papers on my HP Z3100, and they produce completely different viewing experiences, neither of which really met my needs.
The Crane silver rag has a lovely hand feel, an extremely deep d-max with fine shadow detail, and no virtually gloss differential. On the other hand its paper base is a bit warm, so I can't print a black & white image with the kind of toning I prefer (slighly warm shadows and slightly cool highlights) without it looking weird. It basically compels you to print B&W prints warm toned. Of course, this might work great with your beautiful bridge photographs. Finally its surface texture is just a bit too obtrusively artificial or 'non-organic' if you know what I mean.
The Harman gloss FB AI has a very similar extremely deep d-max, and it does a better job of rendering very fine details, especially in the highlights. On the other hand, at least with HP's inkset, the gloss differential is a bit more evident. I also find the paper base just too intensely blue, and it has a boatload of OBA's to maintain that superbright blue/white. The paper's texture is extremely subtle, and is overwhelmed by its glossy reflectance so you don't even notice it; I find it just too shiny. Finally it feels a bit thinner and lighter than its 'grammage' would indicate, and the surface is absurdly fragile. Just brush it with the corner of another print or a fingernail and it's visibly marred.
I've been a lot happier printing on Hahnemüle's photo rag pearl, which simply works better for my photos. However, lots of folks rave about the Harman paper when using Epson printers. I think the only way to figure it out is to have a couple of your favorite images printed on each paper to see what works for you.