Hardest for me to let go of were Pinbot and Strange Science in the late 90s. Super nice examples. I’ve replaced them, but both will need to be restored.
Hardest to sell market wise were Raven and Scorpion.
They may be topped by the Time Warp I have in pieces with no desire to get working. Excellent playfield, but all coils fried, back of cabinet swollen from humidity or water, NOS backglass with minor issues.