Wow, experimental bombers, huh?
What about the XB-51? Just kidding, ugly-ass airplane. I've always been partial to the XB/YB-40s of WWII (and Dale Brown's extension of that with the B-52X Megafortress!) Something about a bomber that just screams don't mess with me.... In all seriousness though, I'd go with the YB-49. I LOVE the Valkyrie, but as an adaptable aircraft , it just didn't have it. High and fast, sure. Nuclear strike, you betcha, but as a precision bomber, it just wouldn't cut it. The 49 would be much more mission adaptable. So its got my vote.