It seems like anyone who goes to both of these parks are bound to compare them, so with the impressions fair in my mind, here goes.
Atmosphere: DL's atmosphere is quaint but could be better. MK's atmosphere is cloning Disneyland, so there's one clear winner. Advantage DL.
Attractions: MK has the better train, treehouse, Splash, Pooh, BTMRR, and TSI. DL has better Tikis, Jungle Cruise, Mansion, Pirates (well, formerly), Fantasyland rides, Buzz, and Autopia.
Here's an opinion sure to stir up some controversey: Although DL's Space is smooth as butter, I like MK's old beat-up one more. So which park is really better depends on what kind of ride you like. I will say that DL seems to be really missing something without Pirates running, and I imagine MK must feel like it's missing even more.
This is going to sound like utter treason to some people, but I have to give a tie here attractions-wise just because while most of MK's missing attractions are scattered all over the rest of WDW, MK has a lot of nice ones that aren't at DLR anywhere for now. I'll take PhilharMagic and Peoplemover and Carousel and even Stitch any day over Storybookland and Alice and canoes and the Indy Adventure (which I don't enjoy, although I admit there's a lot of scenery that's very well done.)
Maintenance: Well, duh. You'll find burnt-out bulbs if you squint at either of these places but DL doesn't have anything as badly malfunctioning as the MK Mansion at the moment. Advantage: DL
Food: This could be won on the Blue Bayou's strength alone, but I don't eat fancy meals in the park but at mid-priced and even at greasy spoon level, DL decimates the dining at MK. Whether you're eating along the river at Hungry Bear or admiring the interior design at Plaza Inn, things are clearly superior. Advantage: DL
Cast: Folks, there's no way to dance around it: the cast at DL is way, way below the standards set by casts from the past 20 years. Entertainers still give it their all, but the other departments are riddled with poor service. Whereas cast at WDW still manage to make warm smiles when you imagine they must be tired of it, DL CMs will commonly give a moment's big cheesy grin followed immediately grumpy look. I had one memorable moment of bad service at the MK (and only one more in the entire WDW complex, btw) but numerous of only two days visiting DL. And the park was nowhere near as crowded and stressed as the Thanksgiving 99 weekend I last visited on. Some people are quite apologetic about it all, but few people are doing their jobs correctly and efficiently.
I'm not going to say this is purely training alone and ignore the issues about salarly, California costs of living, and the fact that DL is simply picking the people they can get instead of the people they want. But to the visitor all that becomes unimportant, so as a visitor I must give the win to MK here.
Entertainment: DL has the better Fantasmic and a slightly better daytime parade, but I'll give it to MK for having less obstructive streetmosphere (for instance, I'll take those banjo guys in MK's Frontierland over the comedy show in DL's that draws a big crowd right at a choke point) and a night-time parade. Also, MK has a heck of an easier time clearing out the park after a fireworks show.
Custodial: I'm mixed on this one. The MK is swarmed with birds but DL is not, so DL should win right there. However, the other WDW parks aren't swarmed which leads me to believe it's not a reflection on WDW cleanliness on the whole. Is there something special being served at MK not found elsewhere in WDW? Until then, bathrooms and trash are both as clean, so tie.
Overall: DL wins out by just a nudge which I feel is appropriate. A larger problem not reflected here is that if you're particularly feeling commandoish, the entire DLR highlight reel can be done in two days and then you're wandering around wondering what to do. WDW can keep you entertained for a week even if you're a cheapskate and don't feel like doing the numerous tours and pay-to-play experiences.
A west VS east thread is so difficult because it's hard to compare the two parks without the rest of WDW (other parks, beautiful hotels, isolated setting, etc) coming into play and outweighing the favor for the MK. I would say that DL is slightly better, but depending on the day (climate, attendance, etc) I'd gladly choose to spend the day at MK instead.
A full-size trip report will eventually appear in the DL forum where it belongs.