Well seeing as how we are arguing about which one is better, and seeing as how I'm a veteran of both parks, I'll give my extended imput.
On the subject of cleanliness. I would both say they are about equally clean. I see about the same ammount of litter at both parks.
You can't say it is better themed and has better rides because they are completely different. It is like comparing apples to oranges when you say a statement so directly. Walt Disney World is a classic and the themes are remarkable! When in Fantasyland, you are only in Fantasyland and are unable to hear or see any other land. Same follows through with the other lands. MGM Studios is incredible in that the theme is present everywhere! Disney does an outstanding job on keeping with the theme. Also, the rides are extremely unique. Example: Rock 'n' Roller Coaster.
It's not completely different. It's more like comparing a tomato to a cherry tomato. I can see where someone could say they like Universal's themeing better. Personally I'm one of those people. With Universal, there will be times where I'm walking through Universal, and the themeing will be say, New York City. There will be times where I actually feel like I'm in New York. The only time I get that sort of feeling is in Epcot. For instance, when I went to Universal for Mardi Grah, my mom and I walked through parts of the New York area we hadn't been to before, and it felt like something strait out of West Side Story or something. Walk by the Twister ride, and there is stuff sticking out of the side of the building. (I'm not kidding either) With Disney I feel like I'm in, well, Disney. And as been said, Fantasy land feels like it was just sort of thrown together, and the NY Street in MGM is a big cutout. Universal put a lot more time and effort into their themeing for those particular things. Sure both parks have their high points and low points when it comes to themeing, but Universal's High points are like, woah.
I also like Universal's lines better. Sure Disney does an AWSOME job with themeing the lines, but Universal does it just a touch better IMO. For instance, if you walk into the MIB Alien Attack ride, you feel like your walking into MIB headquarters. They have the elevator, the little alien dudes that drink coffee. The room where the aliens type on the computer and whatnot. (I hope you know what I'm talking about for those who have seen the movie) It just feels more real. Same thing with the Mummy Ride. When you walk into that line, you feel like your walking into a tomb in Eqypt. Same thing with Poseidon's Fury at Islands of Adventure. When you walk into the Cat in The Hat ride, you feel like you just stepped into the pages of the book. I dunno. I don't get that with say, the Winny the Pooh line, or the Thunder Mountain Railroad Line.
Hotels, I would have to say Disney, yet again I havn't been to the Universal Hotels so yeah.
As for the argument over City Walk and DTD. DTD > City Walk. That's it. End of argument. Why? DTD has more variety. More things to do. Better Resturaunts. And I also didn't have to stand in DTD for 2-3 hours trying to get out of the parks with second degree burns on the back of my legs. My mom and I both agree that that's where Disney won the nightlife thing. DTD is seperate, while you have to walk through City Walk to get out of the parks, and if any of you have tried leaving Universal at closing time during a busy time, (like the fourth of July), you know just how crazy and hectic it can get. For those of you who still don't know what I mean, imagine A LOT of people leaving not one, but TWO theme parks, going through a narrow opening. Yeah. That'll work.

Also the music arguement at Pleasure Island is competely ridiculous. I'm sorry to offend anybody with that, but it's one of the dumber things I've heard in this whole debate. I've spent many, MANY hours in Pleasure Island, and have heard a variety of music, ranging from AC/DC and Motley Crue, to Hilary Duff and Lindsay Lohan. They...play...everything at Pleasure Island. City Walk's choise seems, at least to me, to be a little more selective.
With resturaunts, Universal wins. They don't have as many as Disney, but the few they have, they did extreemly well. From the NBA Cafe to the Hard Rock, its just so good.
But in the end, I would say it really depends on what mood your in. I wouldn't say either is better than the other, because they are both great. I'm just saying, it seems like Disney does a ton of stuff very well, but nothing extreemly mindblowing. (although they are really really good with little kids

) With Universal, they do one or two things extreemly mindblowing, and a few things poorly-somewhat good. Also, as been said, Disney is just so huge. Even with the individual parks, there is just so much to do. For example, I can't even begin to tell you how many times I've been to Epcot, and I STILL havn't done everything. I'm not even close. With Universal, with the exception of one or two shows, and a ride here and there, we've just about covered all of it. In fact there was a time my mom decided not to re-new her annual pass because we have done basically everything.
But I would say if your in the mood for a good, casual, family oriented time. And your in the mood for variety, and a little something for everyone, go to Disney. If your in the mood for a more adult oriented time, and your sick of dealing with little kids, go to Universal. Why? Because....
Disney=
Universal=
Some Things I Missed
-I hate to vouch for Universal's themeing even more, but I would like to say that the themeing in some lines are so good, I refuse to go on the ride because the lines scare me more than the ride. Like Twister for example.
-Disney does have some darn good resturaunts though. For example, Flametree BBQ and Earl of Sandwich.
-The one thing Disney does extreemly well is giving little kids something to remember. If you go to disney when you were at the age where all the charicter stuff and all that was still real to you, that is a memory you will cherrish forever. I love the commercial that was on a few years ago where there was a family, and the only way they could go to Disney is if their youngest child learned to walk. Well they were all frustrated, especially the little girl's brothers and sister's, and finally the mother saw how frusturated the rest of the family was, so she decided to go anyway. Well they were looking at a map or something, and the little girl gets up and walks to Mickey Mouse.