For those who don't want to read my long rant and look at all the pretty pictures, I'll boil this down for you real quick:
MySpace is and ad-ridden hell-hole of a site swamped with crappy layouts, horrendously intrusive marketing, and infested by maliciously insidious users hacking into people's accounts or simply mass spamming you with auto-generated "pretty-girl" accounts.
Yup, that about sums it up. Facebook does none of that, more, and does it right. Let's go along for the point by point, shall we? All images link to full screen versions
Ads, Dear Lord, the Ads
Perhaps you haven't noticed, but the seizures you've been having are MySpace's fault. I can't begin to explain how intrusive the ads on MySpace are. Instead, I want to show you something, you see, I am technically competent enough to swim my way through the shit code that mySpace uses to layout its pages. Using said geek prowess, I have taught my web browser how to hide all the ads on MySpace -- not just the obvious "Punch the monkey" ads, but also the "sponsored content".
Here is a side by side comparison of what it looks like when your not being sold up the river to their advertisers, and when you are being assulted by flashing, blinking, winking, and sexing-you-up ads:

Users: Faked, Hacked, Annoying
Now, I'm not saying that I find all friends on MySpace annoying, but the way the account system is run at MySpace is failing -- horribly. Accounts are hacked on an extremely regular basis and fake accounts are being created even faster, and the MySpace staff can't squash them in kind. I'd like to show you what my Inbox typically looks like after something like only 2 days away from MySpace:

Not one single person in this screen shot is:
- A real person
- A friend of mine
It greatly peeves me that this is such a common problem with the site, because the image is fairly typical for me.
And this brings us to the hacked accounts. Now, I don't doubt the intelligence of any of my friends, but the internet is a tricky place and unless you are as innundated by it as I am, you're not going to catch every single scam and malicious link. And it only takes one before your account is suddenly hacked. Here's a screenshot of my bulletins a few days ago, 3 of these bulletins were not posted by the person who's picture is next to it, but by someone who had their password and was posting it in their steed:

In the past month, 3 people in my amazingly small 34 friend circle have had their accounts hacked. That's a startlingly high figure, and one that MySpace is almost entirely responsible for because people are slipping malcicious code into bulletins that should have been stripped out.
Profiles: The Power, the Abuse
One of the greatest things about MySpace's lack of competent HTML filtering is that it lets through custom CSS code on profile pages. This allows anyone with enough skill to make their page look different from the default (read: horrendously ugly) layout.
Of course, with great power comes great responsibility, and when you entrust great responsibility to hordes or hormonally imbalanced youths, you've made a serious mistake.
Some people didn't go to overboard, I think my profile is pretty sane:

Some people actually spent a lot of time on their profile to make it very appealing:

However, the vast majority of users (sorry Lee!) abuse this loop hole and turn MySpace into a thing straight out of the "Big Book of Designer No-nos":

Between the auto starting music, javascript, tons of poorly coded flash, bad css, truck loads of animating dancing gif, and layouts that make my eyes bleed, the profiles on MySpace are one of the most amazingly abused spaces on the internet with almost no redeeming qualities.
Features: Half Planned and Poorly Implemented
No one can say MySpace is at any lack for features on the site: Video's, pictures, calendars, blogs, forums, group, etc, etc. However, as you will see later on, none of these hold a candle to what Facebook offers in comparison. Some of the comparisons rest solely on the fact that MySpace appears to have been designed by a monkey banging on a keyboard, but mostly the features are barely functional, with no regard to integration or how they fit into the site as a whole package.
Here are two shots which you'll want to keep in mind for later when they are drawn up for comparison, the "album" page and a "group" index page:

Just Fucking Broken
This requires no explanation outside of this screenshot:

Facebook: My Beginnings
I got onto Facebook before it was "everyone can join" days once I got a job at CNET. It was interesting, offered a nice setup, but it was 'closed' for all intents and purposes. None of my friends worked at CNET and because my school wasn't the greatest, getting school based emails was near to impossible -- so I didn't expect that route to work.
Since then, however, Facebook has opened its doors to anyone who would like to join, and as such, there's very little reason to continue using MySpace.
Facebook: Feature for Feature, Hands Down Better
Facebook vs. MySpace, feature for feature, Facebook actually loses, but I don't think users do. See, Facebook doesn't have Forums, or Videos on it -- but I don't think you'll miss these. I have forums elsewhere, and only really care to talk to my groups and friends anyway. Videos? Come on: you ... tube.
However, in the areas that I care about for my social networking, Facebook not only has everything MySpace has, but also does a better job.
- Photos
Not only does Facebook have photos and albums (which MySpace just got), but they do something really awesome with photos -- they allow you to 'tag' them with people's names. In this manner, you can 'tag' yourself and your friends in photos and then find yourself in other people's photos. I think this is a very, very cool extra that you really have to play around with. Here's a screenshot of what it looks like:

- Friends List
You think this is pretty simple. On MySpace, yes, it is. But Facebook takes it up a notch. Not only does it look nicer, but it also treats you nicer and will tell you what each friend has recently updated. That's swell.

- SANE PROFILES
Maybe you really like the profiles being very unique and customized to a persons personality and such jazz -- I can't stand it. Make a video, take a picture, sing a song, make an art piece, but please, please, please -- let me view your profile without crashing my computer from loading 85 5mb gifs along with 12 flash movies and an mp3 background. Really. Thanks.

- Networks & Groups
In the same way that you can join a group on MySpace, you can also do some on Facebook. Facebook also treats "Networks" much like exclusive groups where only VIP's can be. For example, to join the CNET network on facebook, you have to verify an @cnet.com email address you own to prove eligibility. While neither Facebook nor MySpace offers a very clear advantage in the groups, it's certainly not a 'lose' for Facebook.

- Status Updates
Are you a fan of twitter.com? Let people know in a small sentance or two what's going on in your life. Just a quick "Heading to the mall" or "going away for the weekend". It's hard to explain how fun status updates are, so I encourage you to give them a try and see what happens.

- Mobile Integration
If you didn't catch it in the screen above, check it out -- you can have the status updates of individual people sent to your phone. And that's just one of the ways that Facebook allows you to interact with your social networks via your phone -- in a two way manner. I can text in status updates, photos, and new notes just as easily as I can receive status updates. It's a really nice selling point to Facebook that MySpace only dreams about.
Facebook: Where it is Lacking
Now, leaving Facebook doesn't come without some draw backs. First, you can't customized your profile -- this is a negative or a positive depending on your point of view. Secondly, Facebook doesn't have support for music in any way, shape, or form. So, if you use MySpace to run your band P.O.C., etc, then Facebook isn't quite ready for you -- I do, however, hear that this feature is quickly coming. So band heads, check in with Facebook in a month or two.
Conclusion
While not quite ready for a few select groups (bands), the vast majority of users at MySpace would be better served and less inconvenienced by switching to Facebook. Give it a try -- switch over to Facebook, get a few friends to hop over and see how it goes. If you don't like it, come back and tell me I suck, but I can honestly say you'll likely not want to go back to MySpace ... except because your friends are there.
But then, you can be like me, write a nice little article and tell them all to switch to Facebook today. :)