From the way I see it, there are two main reasons people are voting Bug. They either:
-Are afraid of Dragons ripping up CaP
-Like the resistances more than Dragon
Dragons are notorious for being the ass of an offensive force in today's metagame. Stuff like CM Latias and Mence run rampant, and Flygon hits pretty hard too with STAB Outrage and Earthquake. At a glance, Dragon is great offensively and has some decent resistances. However, I honestly think that people are just scared of the offensive powerhouse moves of Outrage and Draco Meteor that they just don't want a Dragon. There is no defined set of rules that make a pokemon a pokemon, as stated by Doug. We don't 'have' to give each Dragon Outrage or Draco Meteor.
We're just discussing secondary types here. I don't think we should necessarily poll jump and predict a moveset that comes with Dragon types. If anything, keeping a balanced CaP in the metagame is pretty important. When casting a vote for a secondary type, things that should pass through people's minds are the resistances, the offensive STAB it would get, and it's general easiness to switch in.
With that in mind, I think Dragon is the better of the two. It would be easier to switch in, have a better offensive typing, and have some pretty nifty resistances, although Bug does have it's share too.
In terms of offensive typing, this is a no brainer. Even without Draco Meteor and Outrage, Dragon's only resist is steel. It would definitely be better offensive wise for this pokemon. Again, we don't have to go overboard with this. The movepool and base stats will speak for itself. The typing doesn't play into this without the moves and stats to back it up.
As for the general easiness to switch in, here is where SR comes into play. Sure, you have things like Zapdos and Salamence, all who have SR weaknesses yet still function well. And it's true -- a mere SR weakness doesn't necessarily warrant a bad pokemon. But there is no denying that SR weakness is indeed something that Zapdos and Salamence hate. Packing more than 2 (2 is even pushing it) SR weaks on a team without a spinner, who suck, will really destroy your team fast if you aren't prepared. I'd also like to note that Zapdos and Mence have extremely high BSTs, and their stats and movepools make up for that SR weak.
You trade Ground and Ice weaknesses for Fire and Rock weakness. However, Dragon gets a Fire and Water resistance as Electric/Bug gets the nifty Fighting resist. Ground, Ice, Fire, Fighting and Rock are all viable attacking types, although there is no SR type other than Rock. The thing that I like about Dragon more than Bug in terms of typing is the actual pokemon that can switch in on them.
So you can switch in Electric/Bug on a fighting move. Provided that CAP8 does not have +108 speed, it will be taken by Fire Blast/Flamethrower from an Infernape when you switch CAP8 in on CC. For Machamp, DynamicPunch's confusion rate makes things unstable, and the two main STAB moves can be taken by Machamp, as it is bulky as well. Machamp can then retaliate with Stone Edge!
I think it's best that some pokemon just have no business with certain pokemon, and I don't really think Fighting types are what Electric/Bug should switch into. Fighting types are quite devastating. Even things that resist Fighting type moves should watch out.
I just wanted to voice my thoughts out, as I really don't like some of the reasoning that people vote some things for. (lol don't even get me started with "because electric/dragon looks cool" bullshit)