As others have noted, the difficulty in ranking and recommending EMs is that their commonality is outweighed by their differences. For example, the sensibility of a fantastic woodrail is quite different than that of a wedgehead.
Asking which EMs are the best is akin to asking which alcoholic beverage or which snack is best. The question is simply too generic. Categories are necessary so that games from different eras with divergent appeal are not deemed to compete with one another. I would go so far as to subcategorize by manufacturer (and perhaps by single vs. multi-player and/or flipper size) since each manufacturer bestows a unique "feel" to the fun factor.
With that predicate, I consider the following titles (listed alphabetically) to be especially successful designs in both gameplay and art [* denotes 3 inch flipper game; # denotes multiplayer game; all others are 2 inch flipper games]:
BALLY:
Capersville#
Cosmos#
Dixieland
Dogies#
Expressway
Fireball '72#
Rocket III
Skyrocket#
Surfers
GOTTLIEB
Atlantis*
Big Hit*
Blue Note/Rock Star*
Hit the Deck/Neptune*
Joker Poker*#
King of Diamonds
Strange World*
Surf Champ*#
2001/Dimension
Volley*
MIDWAY
Flying Turns#
Race Way#
WOODRAILS
Chicago Coin Thing
Gottlieb 1950 Bank-A-Ball
Gottlieb Daisy May
Gottlieb Grand Slam
Gottlieb Harbor Lites
Gottlieb Niagara
Gottlieb Queen of Hearts
Gottlieb Spot Bowler
Williams Sea Wolf
Williams 21
There are so many great EM titles, especially among the wedgehead and woodrail categories. These are just a few that come to mind. I hate omitting so many wonderful titles from my list. However, I see those games on the lists of others who have posted.