Cardboard Box vs Chameleon Safaris?

I'm looking to do a budget safari hopefully through both Etosha and the dunes. Can anyone give pros and / or cons of safaris by Cardboard Box and Chameleon? If I only end up doing Etosha or the dunes, which would you recommend seeing over the other?

What criteria would you use to compare the dunes of the Namib to a game reserve?

I have never used Chameleon but I have organised three trips to Namibia using Cardboard Box and they have been fantastic every time. I thoroughly recommend them.