FWIW, I didn't find funhouse a nightmare to keep running. The stuff going on inside Rudy's head is a bit fiddly to work with when something breaks there, but not impossible, and otherwise it's fine.

I have steered to restoring machines i like.
I rarely break even on a restoration so i always try choose a game i like to play.
Then, i enjoy the restoration and enjoy the machine for a while in my collection.

The best answer I can give is do a game you enjoy. I have and have had projects that just stall out or sit for months. I currently have a Taxi I took in that needs a hardtop or playfield swap. I'm trying a hardtop and I'm finding the whole process impossible to keep on track. I don't mind Taxi but can name 5 other system 11 game I would take over it. Your enthusiasm for the game (at least for me) tends to help keep the project moving forward instead of sitting in pieces in the basement for months.

Any game that you're passionate about is rewarding. Whether you love the theme or if it's a throwback to your youth. Seeing a player condition game (or worse) come back to it's glory (or better) by a passionate collector is hard to beat.

Jaz

You sure you’re not talking about Twilight Zone???

The clock in Funhouse is playfield inserts and computer controlled lighting.

White Water is a beauty when restored.

I would say a Adams Family and a IJ are very rewarding(monetarily) after a restore. Also Fathom and Fishtales seem to fetch a premium after restore. Most restores with the hours involved are tough to break even on.

If you enjoy the learning involved in a restoration, try a EM next. No problem sourcing parts via Pinball Resource.
After restoring a couple of machines from the 80s and 90s , my last restoration was an EM. I learned a ton and met a lot of nice people in the process.
I’ve always held on to my restorations because if I sold them it would be the equivalent of just handing a stranger a couple thousand dollars(and this isn’t including the cost of my time). I could never break even.

The most rewarding restores are when you can take in a really trashed game and turn into something beautiful. Gottlieb wedge heads with all the metal polished on the bottom side of the playfield really look fantastic.

The 90s WPC games are rewarding because they are pretty tired and dirty at this point if you can find one that hasn't been restored. Parts are available like never before including electronics and resale of restored games is high right now. I also love classic Bally/Stern and EMs. They are a lot of fun to play and parts are pretty easy to come by from Pinball Resource and others.

On the other end of the spectrum for me is anything Data East or pre-LOTR Stern/Sega. Junk design, especially DE, is not fun to deal with. Also, stay away from anything with cabinet made out of particle board unless the cab is in pristine condition and a game that you absolutely love.

Anything dead that you drag out of someone's basement that has been sitting for years untouched. I enjoyed restoring GTB System 1 games.