To be honest, I have struggled to find one I've been happy with.
But what I will say is you need a good lance. If you mean the lance included is the one with the grey bottle, it won't work unfortunately. Snow foam lances take in a mixture of air, to create the foam whereas the Karcher lance is more for the chemical spreading side of things.
I bought a lance for under £20 and it never worked properly. You need to buy a good lance and expect to pay up to £50 (or else it won't be much good) and only then I think the snow foams will have an effect. I've bought all the branded snow foam and it looks cool, but never clung to the car it always ran off by the end of the soak time and therefore made absolutely no difference to the cleanliness of the paintwork.
Get a good lance and almost all snow foams will work as well as they should.