I'm not very enthusiastic about the large numbered multiballs like "well of souls" on IJ or 13-ball on A13. They sound cool al first, but all you get is a lot of junk heading for the drain. Almost impossible to keep up a controlled play.
The multiball on Dr. Who is fun indeed. Quite simple to achieve (even for beginners) and you have to hit three different gates to score. Combined with the desparate try to keep the multiplier up with the third flipper it gets really tricky.