I'd have to say
Iron Man: Most games I think long and hard about selling before I do it. This one I kind of just did it without thinking through. I'm very happy with the game I replaced it with, but I do miss IM. The rules became stale, especially the super imbalanced Do or Die scoring and impossibility of DoD multiball, but I miss the battle. Will probably own another one someday...especially now that there are rumors that the code might be revisited at some point. A few minor tweaks would make this an absolute must rebuy.
Avengers: Sold this one out of frustration after not being able to tweak out the last couple issues 100%. It was about 95%, but that last 5% just ate away at me after years of tweaking and adjusting. I absolutely loved the gameplay, but just couldn't let those last couple minor issues go. Would like to own another one someday.
Whirlwind: Love the game, hated the example I had. It was had a nice playfield, but everything else was pretty nasty. It was literally dripping nicotine and stunk bad. I think I got a little bit of cancer ever time the fan blew. I did my best to clean it up, but it would have never been really nice without replacing...well...everything. I'd like a nice one someday.
Honorable mention to CSI, WoF, and BK.
I was thankfully able to fix my two biggest regrets...ST premium I was insane to sell and have since replaced it with a pro, which I'm completely happy with. SM was sold with the intention of getting a nicer one at some point, and that came in the form of a nearly new vault recently. Now I am to the point where anything I sell would most likely end up on this list down the road!
I'm going to go against the norm here and say:
Allied Leisure Dynomite
...all because I spent an unfathomable number of hours restoring each one, and hours upon hours of research and creating documentation for the Allied Leisure and Viza games.
They were ok players, fairly simple games, and fairly rare with very low production numbers. I couldn't help not getting attached to them after spending 6 months or more on each one.
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