I'll help bring this backfrom the dead too.
I agree with most about the WH2O, but for me, its hitting it the 3x in a row when multiball fires up, such a juggle to come out with three and get them back up there.
My second vote was also mentioned - SM venom ramp. However i find it most gratifying to hit it combo'd from the bottom right flipper, around the loop, then up the ramp. That ball comes around the corner with lightning speed, and to hit the upp flipper > ramp is damn near 100% luck!