Carl -- I think you might have intended to post on speedsters, not spyders. Maybe it was that subliminal thing between Danny and spyders.
In any case, people tend to support what they are comfortable with. Danny is a pro when it comes to the Webers, Stan can field strip his Dells blindfolded. I have Dells, that's where my comfort is, and that's what I would recommend (As long as you are OK with the idea that Dells have been out-of-manufacture for years and parts supply is dwindling. In other words if you are shopping for Dellortos you are going to be shopping for used carburetors.)
So which is better? The Dellortos, of course! Actually, they really are. Their progression ports allow smoother off-idle transition, their idle jets are accessible from the top, they have a larger assortment of jets and tubes, their adjustment screw threads are finer for more precision, and the needle valves are more pointed (again for better precision).
How much does any of that matter? None, really. Although the Dells have some technical advantages they amount to just that -- "technicalities". As far as real-world "practicalities" the Webers are equal to the Dells for anything you need.
There is a myth that Dells hold their "tune" better than Webers, but that isn't true. Once adjusted both carbs maintain their adjustment until someone intentionally takes a screwdriver to them. Both Dells and Webers are essentially set'um-and-forget'um. The guy who is constantly tuning on his carbs is almost always chasing problems unrelated to the carbs. The guy who (in a fit of frustration) gives-up on his carbs and replaces them with FI is your new best friend: He now has a perfectly good set of carbs for sale!
So in the end it all comes down to this: Dellortos are better (because that's what I have).