X...because of the confusion of what BB a Roubaix can have relative to model and year, best to post with what bike you are interested in and ask. Its not really straightforward. Will give you an example and G-chopper touched on this. Take the Roubaix Pro that I just built. The 'frameset' ordered from Specialized is threaded...one of the reasons I went with it. The complete Pro bike however is what they call OSBB which is BB30. This is because Specialized crankset that comes on the Roubaix Pro complete bike...the Spesh crank only uses BB30 or PF-30. FWIW all Specialized S-works bikes are PF-30. Given a choice, I prefer threaded first...because I don't put out the watts to need the 1% stiffer BB30
...and prefer PF-30 second. PF-30 is a bit more resilient to making noise for an integrated BB.
Hope that helps.