My first post in this nice forum - so I have to be careful 
EM - El Dorado, since you have to really care about the lit drops, a real shooter
Early - Paragon, itâs about control, inline drops and again control - all this in the beautiful world of Paragon with the Valley of Demons, the Golden Cliffs, the Beastâs Lair and the WaterfallâŚ
DMD - X-Men, three flippers, great tight layout, lot to shoot for (at the right time) and by now a great ruleset
To me, games with variations of the âfanâ layout are best for learning on (as well as keeping on top of your game). Full orbit shots that allow live-catching or loop passing; a variety of shots that have you doing a mix of forward-hand and backhand shots from not just one, but both flippers; scenarios where you will be bounce passing, post transferring and drop catching a lot; games with edge-of-flipper shots, either into important standup target banks or some kind of saucer (i.e., Creature or Fish holes on Monster Bash/Sopranos), etc. Games with stacking being an important factor to scoring high is important as well. I personally feel games like Avatar and The Rolling Stones in particular hit the sweet spot when it comes to practice as any flipper trick can be used and it doesnât take forever to really get things going or to make a great stack happen.
Iâm of the same mindset when it comes to classic SS games as well. Games that require a wide variety of shots to be made in order to score well are important (i.e., games that force you to hit every part of the playfield to score the best, good for practice). Likewise, you need to have a game that makes you use most tricks in the book (bounce passing, drop catching, tap passing, alley passing, backhands and forwardhands, etc). Bally Eight Ball has been a good one for me in that regard.
Always have to have a Lawlor-style game thrown in there to practice as well though. Games like TZ, TAF, RBION, FH, etc., they have a completely different kind of flow than the fan layouts and itâs very important to get used to that style of gameplay too.
If I had to have a five game collection best fit for practice, I would have Avatar, TRS, Eight Ball, TAF, AFM. Maybe remove one of the fan layout games for an EM, as they have a pretty different feel as well.
I really like Jacks Open / Jacks To Open.
The open inlanes mean you really have to have great ball control, plus the very specific shots, which include a number of âsucker shotsâ you have to creatively master to score points illustrate some of the key talents you have to master to do well.
Iâll second this with some specifics. You need to learn to hit not just a target but when to do so face-on vs. on an edge [and which edge] vs. trying to go for two at once. When to not hit a target and go up top to increase target value. When to complete the rack vs. to milk it for max points before going to the next rack. And youâll learn about rebounds and bank shots in the process. On the side drains, you need to learn nudge timing and direction since saves with the mini-edge posts need to be done differently than normal side saves. Itâs a good game for getting comfortable with dead bouncing, too, since itâs slower-playing than most machines which lets players build confidence in this technique â you feel less compelled to flip right away as a reflex since the ball is moving slower.
Volley is another game with similar features and strategies; it came out about the same time.
Good recommendations. Of course, WPT has all this and more! 
Including 2-way orbit loops, 3-second 3x combos, 2" flippers, etc.
and loop corral
Iâll preface this by saying thereâs no way I have the experience of most of the people here, but my RBION feels like itâs trained me in a huge amount of different skills: multiball control for the various modes, staging (for getting the penguin orbit shot with the left flipper while cradling with the right), upper flipper shots, backhands (particularly nailing the center ramp with the right flipper is satisfying when done intentionally), slap saves (depending on how friendly the release from the shrunken head is) and general ball recovery (Europe/tombstone mode).
Only wish I could make it feel/play like a more recent Stern (still feels a little slow compared to them) but in terms of general skills, I doubt I could find a better machine.
These are all great picks.
Mine are:
2" flippered EMâs: Snow Derby, Gator, Beat The Clock
EM - Flip Flip, Volley, Grand Prix
SS - Stars, Barracora, Skateball
DMD - The Shadow, TZ, WPT, AC/DC, I500, Xmen
I can only have 5 in the house and like to have one of each era that I can to practice on. I also have the luxury of having an arcade but if I had to pick one from every era or ones that I play frequently this would be the list.
EM - Atlantis
Nudging, skill shot, accuracy in drops and in shooting waterfall are all super important and it is a game you never get bored of.
SS - Alien Star
The game is fast, brutal but you need to have very good accuracy for the Alien targets, spinner and scoop. And of course great multiball skills and of our the shatz spinner or shatz alien targets is really good skills to transfer to other games.
LSS - Whirlwind
Accuracy on targets to get locks, a quick Inlane scoop shot to practice on, lost passing and banding a scoop, three ball multiball skills and staging the upper flipper for ramp jackpots a lot of goodness for a LLS model.
Early Modern - Demolition Man
I think just because this game is in so many tournaments I tend to practice on it a lot. A widebody that is super fast and you need good accuracy to have success. Has a variety of multiballs and some tight shots to master.
Modern / DMD - Iron Maiden
There are just a variety of shots to master, there is a good depth in rules as well to learn. It is not an overly complex game but I always practice on it as it allow me to transfer those skill to many other games in that era.
I would swap out a 2" flipper EM in there on occasion if possible. (I know you can only have 5). Those games are completely different animals-and contrary to some opinions, are not all just âluck boxesâ. 
Iâm gonna revive this topic and say that Iron Maiden has been a really great game for me because of the two upper flippers, loop passing, tight forehand ramp shooting, and playing a more âcomboâ/âflowâ style on a more modern game. Usually with modern sterns the plan for me is to trap up and control the ball, but with Iron Maiden I find that leads to sub optimal play if I lean too hard on controlled play.
Also, in response to the earlier conversation about lob shots⌠whatâs a lob shot? @bkerins
A lob shot is somewhere between a tap pass and a full flip. Itâs typically used on EMs where thereâs a saucer you need to hit, but a full powered shot will skip over the saucer, like on Argosy or High Hand. Apparently there is some footage of Elwin doing this extremely well on High Hand at Pinburgh 2016, but I canât see to find it.
I agree, I feel like Iron Maiden gives you plenty of opportunities for successful outlane nudging and precision plunging too.
Some machines I think provide a really basic âintroductionâ to modern pinball (i.e. multiball, jackpot modes, wizard modes, stacking/combo shots, countdown shots) are best for new players.
Taxi
The Getaway
Dr. Dude
Diner
Elvira & The Party Monsters
Whitewater
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When I give the pinball class at California Extreme every year, Iâve found Tron, Funhouse, and Whirlwind all have the best elements for me to teach just about any skill with.
Additionally, I like TOM or CFTBL for teaching live catching off of their right loop feeds.
For modern games, Keith has definitely set the trend for games with at least one upper flipper and an upper loop. Games with only two flippers are becoming the exception.
Those older games include the upper flipper and two have loops back to the upper flipper. Anybody notice how many of the new games at TPF have upper flippers and loops? I showed a guy how to stage his right flippers on his new (to him) DE Jurassic Park today and he was stoked.
Toy Story 4 is fairly simple rules wise but is insanely helpful for learning skills on. In particular, this was the game that taught me how to backhand shots with two balls on a flipper (road trip lock during Multiball). Solid introduction game to how most current pinball machines work.
This is what I think of when I hear lob shotsâŚ
Bowenâs lob shots to sparky:
Keithâs lob shot to start TA:
Iâve watched an unhealthy amount of tournament footage and I donât think anyone does them as often as Keith. Either takes the power off of the flip to possibly avoid a high speed rebound, or slightly changes the trajectory of the shot to get a different angle.