Magic Kingdom's soundtrack might get a little saccharine after a while. After all, it would include the cliché of annoying songs, "It's a Small World (After All)."
Epcot, on the other hand, has a rich diversity of international music, stuff rooted in reality, not in lollipops and cotton candy. And its new age/classical selections are superb. Gotta go with that.
Which is precisely why I would choose Magic Kingdom!
I prefer "lollipops and cotton candy", and the "saccarine" optimism and Fantasy of It's A Small World, and all of the Fantasy-based stuff in the MK, over "reality"!
And if MK is tops in my Theme Park, and Theme Park music, pecking order, than nothing is more tops in my MK pecking order than the Fantasy-based, character-based attractions that occupy Fantasyland and Toontown, and the music (both songs and loops) that accompanies them!
My MK fave music also includes the cute, fantasy-based, character-based attractions in other lands of the MK, such as Splash Mountain, Country Bear Jamboree, and Tiki Room.
Of course, MK also has my favorite parade soundtrack, the MSEP, and my favorite WDW Christmas music (from the parade, fireworks, castle show, and music loops)
Of course, the other parks all have their highlights for me as well. It's really hard to pick a second fave, and I agree with those who say the music of Animal Kingdom and the Studios is underated!
Epcot comes in strong with "One Little Spark" and the complete soundtrack to both the first and third versions of Journey Into Imagination (the two versions featuring Figment). Other Epcot musical faves for me include "Big Blue World" from The Seas and the defunct Kitchen Kabaret show, and both versions of the Mexico boat ride.
The Studios comes in strong with lots of songs from the Disney Animated Classics used as BGM in the Animation Courtyard, as well as the soundtracks to the Mermaid and Beauty and the Beast shows, and the awesome Wizard of Oz elements of the Great Movie Ride!
And AK has the wonderful preshow loop for It's Tough To Be A Bug, soundtracks to the Nemo and Lion King shows, and parade soundtracks, as well as some of my favorite instrumental BGM loops at any of the parks.
Here is a more comprehensive (though not complete) list of many of my musical faves from MK, Epcot, Studios, and AK:
Magic Kingdom
It's A Small World
Winnie the Pooh ride-through and area loop
Snow White's Adventures
Peter Pan's Flight
Mickey's Philharmagic soundtrack and queue loop
Mickey Mouse Revue soundtrack (defunct)
Cinderella's Golden Carousel loop
Dumbo the Flying Elephant loop
Mad Tea Party loop
Pinocchio Village Haus loop
"Merilly Song" from Mr. Toad's Wild Ride load area (defunct)
Mickey's Toontown Fair loop
WACKY Radio loop (from Minnie's House)
Splash Mountain ride-through and queue loop
Country Bear Jamboree soundtrack (for all three shows)
Big Thunder Mountain Railroad area music
Enchanted Tiki Room (original show and parts of the current)
Tiki preshow area "Tiki Lounge music"
Swisskapolka (from Swiss Family Treehouse)
Magic Carpets music loop
Yo-Ho (A Pirates Life For Me) from PotC
Adventureland main music loop
Carribean Plaza steel drum loop (now heard only from a few speakers near the usually closed El Pirata counter-service area near Pirates)
Carousel Of Progress Soundtrack
Tomorrowland music loop
Star Tunnel entrance music from Space Mountain (heard here!
http://www.youtube.com/watch?v=F975mpnbg-I)
"Galactic Anthem" load music from Stitch's Great Escape
Sonny Eclipse songs from Cosmic Rays
If You Had Wings theme song (defunct)
Main Street Music loop
Welcome Show and Trolley Show
Main Street Electrical Parade
Wishes
Spectromagic
Main Street Christmas Loop
Holiday Wishes
Once Upon A Christmastime parade soundtrack
Fantasy In the Sky (NYE fireworks show)
Celebrate the Season Castle stage show
Epcot
Journey Into Imagination "One Little Spark" theme song, ride score, and area loop (current and original versions)
HISTA load music (defunct?)
"We Are Here To Change the World" and "Another Part Of Me" from Captain Eo
"Big Blue World" and score from The Seas with Nemo and Friends
Soarin' score
Kitchen Kabaret soundtrack (defunct)
World Of Motion soundtrack (defunct)
Universe Of Energy score (current as well as original defunct songs)
Innoventions area music
Gran Fiesta Tour soundtrack
El Rio del Tiempo songs/score (defunct)
Mariachi Cobre
Spirit Of Norway load music and score
Spellman's Gledje (defunct)
Reflections Of China score/load music
Si Xian
Octoberfest Musicanten
Impressions de France score
British Invasion (especially when they play selections from late-period Beatles, such as the Sgt. Pepper, Magical Mystery Tour, and Abbey Road albums)
Music loops from all 11 countries (favorites are Mexico, Norway, China, Germany, and Japan)
Illuminations preshow loop and main show soundtrack (especially the extended Christmas version)
Tapestry Of Nations (played in it's entirety around the lagoon after Illuminations)
Disney's Animal Kingdom
Oasis Music Loop
Tree Of Life Music Loop
Discovery Island Music Loop
It's Tough To Be A Bug preshow loop (can be heard in it's entirety here, with no crowd noise! -
http://www.youtube.com/watch?v=of16p1xPiKc)
It's Tough To Be A Bug theme song
Festival Of the Lion King soundtrack
"Colors of the Wind" from Pocahontas and her Forest Friends show (defunct)
Africa Music loop
Habitat Habit music loop
Flights Of Wonder score and preshow music
Asia music loop
Everest music loop
Finding Nemo: The Musical soundtrack
Mickey's Jammin' Jungle Parade
Mickey's Jingle Jungle Parade
The Tropicals steel drum band
Disney's Hollywood Studios
Fantasmic! Soundtrack
Magic Of Disney Animation area music
Walt Disney: One Man's Dream area music and film score
Beauty and the Beast musical soundtrack
Voyage Of the Little Mermaid soundtrack
Playhouse Disney: Live on Stage soundtrack
Star Tours area music, "droid rooms" music, and ride soundtrack
Great Movie Ride lobby music and ride through music (fave parts are the Mary Poppins and Wizzard Of Oz parts)
Honey I Shrunk the Kids Movie Set Adventure music loop
Muppet Vision area music (especially "Rainbow Connection")
Stars and Motor Cars parade soundtrack (defunct)
Osbourne Festival Of Dancing Lights soundtrack