Both are OVA with old style of animation. In both, the main character is young, perverted male with close to no shame ho is helping females and causing them fall for him. While Golden Boy is heavy ecchi, Dragon Knight is hentai. If you liked one, be sure to check the other one.
Both anime titles take place in a similar fantasy world with magic, swordsmen and monsters. Both have a lot of comedy and action. Dragon Knight is much more ecchi and comedic while Bastard is more violent and has more action. Both anime where also created around the same period (early 1990's) with similar animation and a similar tone. If you like one, you should enjoy the other.