kk Time for me to work :D
First I'll take a look at the stats and how they use them.
From what I see, Drapion has a 5, yes a whole 5, BST advantage! Drapion has slightly more bulk with that 110 def, even though it HP is lowered. It also has slightly less physical attack to Nido. That said Drap is considerable faster than the King. Basically, it's just what you need for your team. You seem to have the bulky thing fine, but not a whole lot of speed. I'd say Drape for this bit just for the ability to hit faster and take the extra physical hit.
Next, I'll be looking at what sets to use in-game.
Drapion has a very good moveset, and you can easily get the moves you need from just TMs or even just Lv up. It is tho, useless with anything but physical moves. I guess in-game special doesn't matter to much, but if you have special covered, make it physical. Some of the moves it learns..
There are a fairly large amount of combos to go with. Having one weakness helps by not needed as much coverage, Ice fang provides good offence against the Grounds and Dragons. Toxic spikes isn't as good in-game, but if helps against the E4 who use several Pokemon, and not just one little pidove.
KK lets go Nido.
Nido has a much lower natural movepool, but it gets everything it needs from tutors and TMs, so that shouldn't be a huge problem.
Again, it can provide a large amount of sets to keep your enemy guessing. Surf is a bonus too, so you don't have to use it on your water Pokemon if you don't want to.
Nido is a slower but bigger hitter. Although Rivalry and Poison point have little use, both are decent ingame. Sheer force is great to use tho, and should be if you can. Drapion#s abilitys are both very useful. Sniper combined with Razor claw and night Slash have a very good chance of dealing x3 damage. While you can avoid being hit by crits altogether with battle Armour. Both have got some good HM usefulness, but if that's all you want them for go find something else more dedicated.
All round, I'll say Drape since it synergizes better and can deal damage faster. (and to make sure Pm doesn't smite me)