The worst was easily the Gottlieb Pro Football that had a body so ridden with termintes, the legs held it together ! Yes, I'll get back to the resto soon !
The best was easily my Paragon. I saw it removed form the container (NIB) as a child, I played it during my youth, my father gave it to me 10 years ago "to keep"
and it sits in my Gamesroom - as the centrepiece of my collection. Since I never really PAID for it, technically it is no a "purchase".
Sooo.. My "Holy Grail" was a Fathom. I bought it off eBay in Germany, had it air freighted to Australia, and it is in storage, awaiting restoration (new playfield, plastics etc !).
I would like to think that my "best purchase" has not yet happened !