Favourite also would definitely be spinner, although inline drop targets would be a close second.  Favourite hammering of the spinner would likely be on the Bally Freedom.  Although I have the SS version, I played the EM version in my youth, and the satisfaction of nailing the spinner (and this game had spinners on both sides of the PF) was right up there.

In-line also a favourite, and remember again in my youth playing Future Spa heaps of times.

It has the "combo shot" that has not equal in pinball. From the right hand in line drop target, the ball runs onto the flipper for a HARD shot to the top of the playfield where the second in tine target bank is. So if you knock down all right hand drop targets to release the first captive ball, when that ball ejects, and all but one top in line drop is standing, you can knock that over and have 3 ball multiball. Really hard to obtain, but this shot is my favorite in pinball.

Nino, not the only way to do this.  I had the great opportunity of playing this pin at a recent meet, and played it for hours.  In fact, I found the easier way to hit the top inline targets was actually with the bottom right hand flipper.  Not an easy shot, timing is everything, but more chances this way than trying with the top right hand flipper.

I defy anyone to have completed the inline drops on Centaur.. best ive done is 1 remaining.. absolute killer of a way to achieve multiball

Totally agree with you Gav.  Centaur was also setup right next to the Fathom at the said meet, and also played this game for hours.  Really enjoyable game, I must say.  And yes, the inline targets on this one are very, very tough.  Most balls I only mustered one, maybe two targets.  Just once the whole night did I actually drop all of them, but a very rare occurance.