Duke is nice and soft and does press against the prostate nicely, as does the G-Rider (extrapolated from Ridge Rider). The G-Rider is probably a better choice if you want to "actively" rock back and forth, as the Duke is a bit harder to work by hand.
Duke has nice, throbby vibes, much more all-encompassing than the G-Rider. Duke is also much easier to clean - while the bullet still isn't waterproof, it's easier to remove and looks like it might be able to tolerate splashes better than the Nexus bullet. It lasts a long time between recharges as well.