Check out both...
A CSIA Level I course will set you back 300 bones at the very most, depending on where you take it, and gobble up 3 days of your time. Learn more about it at www.snowpro.com
If you have the love of skiing, this will be money well spent, even if you never teach a single lesson. Think of it as a 3 day ski lesson with a top level ski teacher.
The CSPS (Canadian Ski Patrol System) is an amazing organization, training "volly" patrollers nationwide. Their training regimen is impressive and exhaustive. Patrolling is not an easy job, especially in this era of easy access to big air and the fashion appeal of being "extreme". They look for strong skiing skills and do in fact, have a testing standard that candidates must achieve before being accepted into the ranks. This, of course, in addition to the first aid requirements, guest service skills, communication skills, understanding radio protocols and having the willingness to do the less glamorous jobs like putting up fences and warning signs.
So, back to the beginning... take the instructor's course, and then if you decide teaching is not your thing, you still have some transferable skills that will serve you well in your ski patrolling career.