Droidekas are savage, and excellent point defense units. Assuming there's a screen of smoke or suppressing fire or something to cover them as they roll into position, they also make highly effective assault units. They have their weaknesses, as do all things, but assuming they are used properly, they massively outclass SBD's.
SBD should lose its shields, as not only are personal shield generators extremely rare, SBDs were also all about higher hull integrity. They were supposed to be durable in contrast to the flimsy and weak Battle Droids. Droideka have decent hulls, but vastly inferior to the SBD; their strength is in powerful deflector shields.