I've had both - the Sansamp will give you the 'wooliness' and dirt of the SVT rigs very easily, but that's pretty much the only sound I could get mine to make.
The DHA will take a bit more getting used to, as you've got the 'mid' and 'Q' control too. I prefer the DHA, as it has loads more features (DI out, line in and headphone socket) for roughly the same money, but ultimately it's your choice.