1. I find zaino easier to work with. Klasse goes on easy, and is very easy to apply in thin coats, but can be difficult to buff off. There are a few different methods out there people have for removal to make it easier, but no real textbook standard.
2. Zaino beads water, KLASSE sheets. This is a matter of preference. Some people prefer beading so they can tell when it is time to rewax, while others prefer sheeting to try and minimize water spoting.
3. Shine is very similar. Zaino has more of a clear, glassy, reflective shine as if the car was coated in glass. KLASSE seems to tint the car redder, blacker,etc,etc, and make it look like a "wetter" reflection. My dad actually likes that KLASSE makes his blue caddy look a shade darker.
4. Slickness - zaino wins hands down
5. Prep - zaino is non abrasive so the surface should be properly prepped before it is applied. KLASSE AIO tackles most of this in the one step.
With that said, there are a number of users that use both with great results. Most klasse users find the need to top with a carnuba to seek more depth, while zaino users seem to enjoy just layering it to infinity. My biggest complaint with Klasse is lack of a contact for customer support to answer the questions we all have on the removal, curing, drying, layering, and hazing. The product has been around since the 1970's, so one would think that all this stuff would of been documented and sorted out already. Luckily some of the top dogs on this board have done enough experimenting with it that it is mostly all sorted out. This board is a great resource.