If we're looking at all genders, I would say my Female Hydreigon. I managed to get 31 IVs in HP, Def, Sp. Atk, and Speed while it got a Timid nature. It's Sp. Def is also around a solid 23. I actually got another male Deino with the same set-up and a Modest nature and both have Dark Pulse, but I don't know what I was on at that time because now I don't know where it is. It may have either gone to my dad's game or I was dumb enough to delete it since I didn't know I could get wi-fi at the time.
Honestly, if it's only Males, the breed I'm proudest of as far as future breeding is concerned is my male Druddigon. It managed to get 31 IVs in HP, Atk, Def, and Sp. Def just like my Mach Punch Conkeldurr. This really opened some new breeding possibilities for me in the Monster and Dragon breeding class. I would want to be proud of the Eelektross, but it turned out Female, which is a shame because it could have been really useful for pokemon in the Amorphous group.