From all that I have read and as to the current price of used Bronica equipment - go for the Bronica! The Kiev is a crap shoot, you may or may not get a descent piece of equipment. Whereas, those Bronica SQ-A users I have talked to, swear by them.
I could never save my pennies fast enough to get a SQ-A system. I wound up with a Fuji rangefinder, which fit my method of madness better. Now I have two so I can be twice as... But I still sometimes feel the urge to get a Bronica.