I have both the Sansamp DI and the MXR DI. I find The Sansamp DI to be my choice when going straight into the board. The MXR's construction is a little more robust, but the distortion on the MXR is a little more harsh and not as "tubey" or warm as the Sansamp. They both sound great through a rig.

My fav setup: Stingray->Sansamp->SWR 350->Goliath->RE20->Great River