I rarely demo anything, but whenever I do, I use the Tech 21 Sansamp my bandmate has. I believe we even use the stock EQ and Cabsim in his DAW? But this is something I want to learn more about down the road.
For metal stuff I use Mammoth by arorua DSP, the built in amp Sims sound quite nice. For anything else I either use the direct signal or a use a SVT amp head sim (without the cab) from a zoom b1x four multieffects