Never heard of PILLOW ball susp. however PIVOT ball is basically slop free and thight like a tiger!
Its a matter of personal preference, driving style and support.
Mugen is on a wave these days, xray havent been winning anything major lately, except for "readers choice awards".
Not to many here have tried both, and if they have they tend to reccomend the model they currently is driving.
Between xray and Mugen you cant go wrong. drive them both and make your choice...