Actually, there are too many favorite bits, and it may change every day!
Some which come to mind:
Probably Trick of the tail has the most numerous perfect moments, with Oldfield's Amarok:
robbery assault & battery: the prog part
entangled: the end
ripples: the instrumental bit
los endos: after the extreme drums & bass intro: the floating keyboards.
mad man moon: after collind say: "sun & sand"
dance on a volcano: the part where the bass is at its highest speed, just before the end.
Collage: moonshine @ 10:30 the hackett-esque guitar sound (spectral mornings)!
the many changes on "in your eyes"
Many parts on Oldfield's Amarok.
Camel's nude: the keybords part on beached or docks (I do not remember which one)
Gilmour's solo on Supertramp's Brother were you bound.
Banco's Traccia 2.
Triumvirat's spartacus: the second part of this track.
The prog part od Rush's circunstances, after the small bells.
the jazz part on villa strangiato
the electrifying guitar solos on rush's power windows.
the piano on wakeman's statue of justice.
many many keyboards parts on eddie jobson's green album
zappa's redunzl, bogus pomp, drowning witch and inca roads
IQ: the beginning of fading senses & further away including the fretless bass
on further away, @ 8:25: this rutherford's smallcreep's day keyboards, followed by crystal clean melodic acoustic guitars & keyboards.
leap of faith: when the keyboards enter after 3 minutes, till the end
the mellow end of darkest hour.
seventh house: when nichols says "cathedral the man created"..., and from 6:35 to 11:30: absolutely delightful!
wrong side of weird: from 8:50 to 9:45: a great prog moment!
narrow margin: from 5:15 to 8:00; from 9:05 to 12:00; from 13:00 to 15:35: it is a watcher of the shy-esque prog part; from 18:00 till the end: an amazing mellow & emotional end!
failsafe: from 3:15 to 4:25; from 5:57 to 6:30;
speak my name: the fretless bass + piano on sleepless incidental
tunnel vision: the new age keyboards + bass from 5:00 to 7:10
intelligence quotient: from 5:15 till 6:50, it is one of my favorite moment of IQ!
capital letters: from 1:35 to 2:17: the bass is outstanding!
about lake 5: from 2:20 till the end: this Camel-esque bit is absolutely wonderful: listen to this wonderful fretless bass and the bluesy guitars!
I should add many bits on wake, lush attic, nomzamo and sitting comfortably!
Actually, every time there are fretless bass, I really enjoy it at its maximum!
So, i also like Eloy's fretless bass on at the gates of dawn (planets)