I currently have my 2012 360/12c63 strung with TI Flats and my 1991 330/12 with Pick of the Ricks Compressed Rounds. The feel of the two guitars is remarkably different, as you would expect. But, contrary to what one might assume, the flats are low-tension and very easy on the fingers. They also happen to intonate well with a 6-saddle bridge and to last years. All of these observations have been made here many times before.
As for tone, the TI Flats dull the sound of each fundamental (low) course and thus accentuate the sound of each octave, to produce a more treble-heavy, jangly, sound, with a clear sixties vibe. The compressed roundwounds don't sound as harsh as the various brands of regular roundwounds I've tried over the years (including D'Addario XL's and POTR Curt Mangan Fusion NIckel Matched). For obvious reasons, the compressed rounds produce more rattle than the flats, particularly when played through a JangleBox with the JangleBoost engaged. But one could argue that this is part of the classic Rickenbacker sound.
I like having different string sets on my two Rick 12's because the guitars play and feel and sound so different from one another. String choice all depends on what tone and feel you're looking for, so finding the right strings may take some experimentation. With the exception of Pyramids (which have gotten some rough press here), I don't think you can make a mistake following any of the suggestions in this thread. Happy string-hunting and good luck!
Robert
