Not that I have any scientific info to back it up, but assuming we're talking about fairly high quality stuff here, I would think unicrown forks, ugly as they are, are generally stronger than lugged crown forks. The tubes are fat, which makes for a strong, stiff fork. In the early days of mountain biking, lugged crown forks had a well deserved reputation for being more "compliant" than unicrown forks, because the fork blades would flex more for a more forgiving ride. That's good sometimes, but in terms of the strength of the fork, I think the flexiness is telling.
I've got a "double plate," lugged crown fork off of an early Shogun Prairie Breaker mountain bike. I think it's the coolest fork I've ever seen. These "double plate" lugged crown forks were supposed to be the strongest design for a lugged crown fork. They basically have two plates instead of one at the crown, one on top of the other with a gap between them. I think some of the early Bridgestone mtb's had this type of lugged crown fork for awhile.
As to whether a sloping crown like the one shown on the Raleigh Professional would be more prone to failure than a lugged crown fork without a sloping crown, I don't know-
Last edited by well biked; 06-30-07 at 08:01 PM.