I am looking into getting a RB67 and was curious what prism to look for and what the differences are? I already have an old Rollei and want to avoid using the waist level finder.
A waist level finder would be messy for vertically oriented shots to be sure. I recommend a meter prism. That will give you the additional functionality of built in metering.
I agree with "fmw" and it has the great advantage of improving your muscles. The basic camera is heavy and with the meter prism, it is one of the heaviest hand held cameras around. Otherwise I used to use one in preference to my Hasselblad due to its image shape.