I agree that all competent spin training is good but I'm a bit surprised that you'd put the C150 and C172 in the same category. While there are many aircraft that will spin more satisfyingly than a C150, it does at least try, and the elements of classic entry and recovery technique can be demonstrated. Like Westhawk, I've found the C172s I've flown to be quite hard to spin, and they more or less sulk their way through the procedure. No doubt it's still a useful demonstration of the flight characteristics of a C172, though.
In terms of 'easy and fun' I'd also put in a vote for the Decathlon - guaranteed to leave you smiling!