Have done both schools multiple times, and to some extent it's apples and oranges. The schools differ in what's taught, how it's taught, how it's drilled, how much detailed background info is given, the skills and attitudes of the typical students, how long the schools are, and how much they cost.
If I had to pick one or the other as a single once-only class, and if money is no object, then the answer is obvious - Spencer's school will make a much bigger impact on your riding, and the total package is much deeper and more coherent. Absolutely no question - if you can afford the entry fee, you'll walk away a changed rider with a huge new set of riding tools and a different attitude.
But since one Spencer's school costs as much as 6 CSS schools, it's a little unfair to compare single schools against each other. And there are some excellent concepts and specific skills that CSS teaches that you won't get from Spencer's schools, along with a different point of view about riding that's very valuable.
Kevin Schwantz's school is another option that's very good, closer to Spencer's school in terms of depth and time and cost but teaching slightly different things in a different way. However it's not as personalized as Spencer's school, and is geographically undesireable for folks on the west coast (though Road Atlanta is an awesome track).
Take 'em all if you like to learn and have the disposable income. But if it's any guide, I've gone to Spencer's school 5 times, CSS 3 times, and Schwantz once. I haven't taken any schools in about 3 years, but I did just sign up for another Spencer's school in December - partly to brush up on skills, but partly for fun since I didn't get to do much track riding this year and I need a good solid fix.
