I don't own a SL66, but I would say that if cost is no object and you plan to use it primarily on a tripod without a flash, it will probably best the Hasselblad. It seems like it has become a cult camera among landscape / nature photographers due to the built in tilt and easy macro capabilities. If you primarily shoot people, however, I would opt for the Hasselblad due to the leaf shutters and superior handling off of a tripod.

I own a Hasselblad, because A) accessories are surprisingly affordable if you are patient and keep your eyes peeled, and B) I use it both handheld and with flash regularly. If I want movements and a camera on a tripod, I use a 4x5 (rarely).