Since I am a huge fan of this generation and this thread came up again... here we go...
1. Fathom - "the pride of creation"; two inline drop target banks with a kick out hole to lock balls... and on top they can be remotely "controlled" by another drop target bank. Then there is a spinner, which can give huge points, especially when lit during a two or three ball multiball. Furthermore a "hurry up" extra ball shot after shooting on another drop target bank in 1-2-3 order. One more thing to mention - a very nice "satisfying" combo... left flipper - cave trap drops, upper right flipper lagoon cave drops (or kick out hole)... (now I have to stop )
I am pretty sure that this machine was only possible because of the huge commercial success of machine like Harlem Globetrotters, Kiss, Star Trek, etc. one or two years before - but okay that's another story!
2. Eight Ball Deluxe - maybe the best single ball machine on this planet. Beside the layout there is a nearly perfect ruleset.
3. Centaur - the most unique and innovative pinball of all time (my personal opinion). Self ejecting (up to 5!) multiball, echo board for even improving the super cool sound, captive ball for inline drop targets, magnet which holds the ball, "hurry up" (multiplier) bonus collect shot and some say the best (at least coolest) artwork ever... Only my personal number 3 because of the not perfect ruleset - but still it is very good. I also miss a spinner or playfield multiplier.
4. Flash Gordon - hey, you need skills and a plan to have fun (and points) with this machine. And that's exactly why I love it! The artwork is also very nice - it is a shame, that nearly cabinets are totally faded. It looks great in original red. That's the only multilevel design I really like.
5. Star Gazer - a unique design (in the usual sling area), the best spinners in pinball history. Nice rule integration for the middle spinner and the drop target right beside. I also love the way a lot of early Sterns redirect the ball.
So now it is getting hard to find an order
6. - 9. (alphabetically )
Future Spa - complex layout, nice ruleset, super fun to play
Harlem Globetrotters - one of the best players, a true battle machine in competition but compared to the top 5 it lacks of features
Paragon - which pinball machine has Golden Cliffs, a Valley of Demons, a Beast's Lair and a Waterfall Lane. It must have been a lot of fun to design this pinball. In terms of details and artwork a top 5 machine. And it has one of the toughest shots ever - the kick out hole (5x/extraball) which is protected by a little plastic which denies clear "perfect" shots.
Seawitch - turn it on and you will the sound of waves, how cool is that ? A superfast player, nice integration of the drops!
The 10. place - not sure, so the is an incomplete honor roll for other outstanding pinballs
Frontier - "ugly", but a challenging machine with the best "indirect" bonus collect shot.
Viking - a little bit unbalanced, but the absolutely best bonus collect shot - left flipper to the kick out hole on the top left side... sounds easy, but check out the way the ball has to go
Barracora - as you have seen til now only bally/stern... and there could be even more of them... okay Williams did a great job on this machine - design, layout, multiball - fun! Firepower 2 is also close, especially with the drop target upgade.
Black Hole - such an amazing pinball machine. Gottliebs masterpiece - but still, I do not fall in love with the Gottlieb solid states - can't tell why. Maybe first of all because of the way the ball flows on this impressive Sys80 widebody lineup. A friend of mine has a nearly complete Sys80 lineup. That looks so cool having them in a row - but still no greed to get them.