Right now, a Sansamp ParaDriver. It's a great DI, and a fair preamp in front of my YBA-200-2 (passive EQ on the head). But things sometime get boomy, and while there's a lot more depth, I feel like I'm loosing a bit of liveliness. Then again my strings have been dead for months.
Really, I just want to get a local electrical engineer to take a look at my head and see if he can basically replace the preamp, or at least mod it for Boost/Cut EQ. That might eliminate my use of the PDDI in the chain (have to see how the active EQ on the head affected my dirt pedals in comparison to the PDDI), but I'd still keep it around for studio purposes.