Quoted from fireball2:
Having owned 18+ ems, worked on dozens more, and played hundreds, these are my recommendations...
Everybody has seen all those damn Gottliebs everywhere. Go with something different.
Space Mission (or Odyssey) (great gambling game)
Grand Prix (great gambling game)
Mars Trek or another Sonic game
Almost any Steve Kordek designed machine
For short flipper games
San Francisco (great gambling game)
Oh Boy (THE BEST gambling game)
Almost any reverse wedgehead from Williams in the '60s
If you want a woodrail go with Balls a Poppin with 7 ball multiball! or (Gottlieb) World Fair
Nip It is groovy enough
The Original Fireball is a good gambler due to the randomness of the disc
1970 Bally Expressway is a great choice. However, the OP is not likely to find an ultra-scarce Bally Balls-a-Poppin and he specifically stated that he disfavored 2 inch flipper games.
Bally Skyrocket is fantastic, albeit pricey at the moment (approaching the $3K mark for an unrestored example).
In my opinion, the best 3 inch flipper Gottlieb wedgeheads, which are somewhat available and affordable, are Volley and Atlantis. Volley is drop-target nirvana.
I might be willing to sell my collector quality Volley. Just be sure to get a true production Volley as opposed to the cheap painted chipboard playfield Volleys out there.
I also love Blue Note (very low production), Strange World, Hit-the-Deck (low production) and Big Hit in my line-up, all 3 inch flipper titles. But, the 1st three titles (BN, SW and HtD) are commanding high prices (the last two Strange Worlds sold for about $3,800 and $4,500 and HtD and BN have traditionally fetched high $$$). Big Hit, while still affordable, has become hard to find.
Succinctly stated, I recommend Gottlieb Volley, Gottlieb Atlantis, Gottlieb Big Hit and Bally Expressway as the best bang-for-the-buck games, which are reasonably available. None will be super easy to find immediately. Nevertheless, these titles do appear for sale sporadically in the $700 - $1,800 range, depending on condition. These CQ wedgeheads will fetch north of $2K, especially Atlantis, but closer to $2K than to $3K generally. These are fantastic games, with smart playfield designs, pleasing shot vectors and attractive art packages.
All will probably hold their value or escalate, based on a 35 year trend and in light of recent EM price trends. Been in the hobby for over 3 decades. That's my 2 cents.