I've had both and yes, both are awesome bikes. But for me, the SG is the one. Radio, wind protection, killer looks, etc. Can't go wrong with either one though!
having had my SG for 53k now... I think that I would go with the RK, but add a detachable bat wing with stereo to it and also have a regular windshield.
Road King all the way. I don't like fairings or need a radio (yes i have a detachable fairing so I know what I am talking about). Plus out of those two bikes the SG's bigger front wheel is a turn off.