Man... This is a tough one, because I own both EHOH and an Maiden Prem. Both of those are dream themes for me, so I will be pretty biased when it comes to how I talk about both of those!!!!!!
I also want to own a Batman 66(preferably catwoman edition) one day.

As for art, all 3 have one of the best art packages ever. Can't go wrong with any of them. Its really a 3 way tie. I do prefer sex appeal, so Batman and EHOH have that in spades, but I love Eddie and I love Iron Maiden and while not sexy its about the coolest thing ever for me. So 3 way tie.

Code...
As of right now I think Iron Maiden has the best code. And I think for me. Even though EHOH code is becoming amazing and super deep, and Batman 66 is super deep as well, I'm going to go with IM!!!! The reason is Batman 66 has a lot of things that while cool and unique I don't really enjoy about code, and perhaps even too deep for my tastes. Not saying that its a bad thing. But, I think Maiden is a nice mesh of old school design with modern elements in it. And the modes really stand out and have a personality, and they feel unique and do a great job implementing the various shots.

EHOH I don't feel that way. To me its just this is lit then shoot the next one. Then the next. No real personality to the modes. But, I do love the fact that it has non mode scoring in it like, unhappy hour and drive me crazy.
Batman 66 I'm not too familiar with the code, but I always love shooting it!!!! You can't go wrong with any of these, but Maiden goes more right!!!

Layout...
Iron Maiden has the best layout. Its a unique layout, that also is really smooth and fun. Very challenging as the ramps are some of hte harder ramps I've come across in my playing. They look so simple and easy... But, you really got to get dialed in to hit them consistently. Its possible and when you are the game feels so good.
EHOH I like the layout, but it is a standard fan layout. So while its amazing and I think shoots great. Its something we've seen before.
Batman 66 is a little unique, but its a bit clunky. Nothing wrong with that. Its very fun to shoot, but a bit clunk fest.

Mechs or toys. Maiden doesn't have any. It has sculpts... But, I still think the sculpt for piece of mind wasn't designed properly. To see any detail you'd have to look at it from the underneath angle... I get the pose is hunched over, but they could and should have tweaked it to where more detail is visible in the sculpt. A very rookie mistake.
As an artist should know how their work is being displayed and adjust it accordingly... For instance Michelangelo's David has huge HANDS(and we know its not true what they say about huge hands as he's naked!!!), but that was because he was meant to be displayed up high on a building top. So the hands had to be slightly out of proportion for them to register from teh distance and angle.
Still not convinced... Well. Got one that is AMERICAN for ya. The Lincoln Monument the artist designed it with a certain type of light in mind. And when he saw it light up(or in his case not light up) he was appalled at how it looked and he demanded they put in lights to make it match his vision. Of course he directed and instructed where the lights would be. This all matters. And the sculpts on Maiden were lazily designed.

Batman 66 has toys. The crane of course. Interesting toy. But, also the batcave, and the phone and the tv. Those are nice.
But, EHOH has the house and the crypt and those are some of the coolest toys in modern pinball. Not the coolest as that goes to the T-rex from JPark and also runner up the black Knight from SOR. Still... EHOH really enhances the theme and wins on the toys.

Music... Well Iron Maiden wins for me. THey're my favorite band of all time. Seen them 6 times live. But, EHOH has nice music that fits gameplay too.

Light show... I don't know man. I'm easily impressed with light shows. I was impressed by my Night Moves light show. So I don't know. I only know a bad light show when I see one. Otherwise I'm like... WOW A YELLOW CAR!!!!!!

FUN! I think its a 3 way tie. All games are really fun. At least to me.

So. Which game is the best. I'd say barely Iron Maiden wins out. But, you can't lose between any of these games. I love my EHOH and its really going to be a great game when the code is finished.

Its looking like its going to either be a Ghostbusters or a Batman 66 as my next pin purchase. So I mean... I really do want a batman and I plan on getting one eventually. Just a great theme, great looking game, and plays great!