Ok...I really don't understand why Fuzznip (and everyone else) dislikes Fighting/Electric, so maybe I will detail why it is a good choice, since no one seems to be doing that?
Defensively: The Electric secondary typing "only gives it a resistance to electric type moves". That's true, but maybe it should be put another way: "The Electric secondary typing gives a resistance to electric type moves!" That's better. Why? Firstly, Rotom-A is Togekiss' biggest counter for one reason: STAB Thunderbolt. Togekiss is immune to Shadow Ball, and has the Special Defense to take an Overheat and Roost it off easily. Now, between a Fighting/Electric CAP11 and Togekiss, if predicted correctly, all Rotom-A can do to hurt you is a WoW, which is a problem with any secondary typing at this point. And what's the worst case? CAP11 takes a Shadow Ball, which hits it neutrally! A Fighting/Electric CAP11 can handle Rotom-A better than the vast majority of OU (Pursuiters excepted, of course). Also, Electric STAB hits Zapdos neutrally, which is better than just about any other type mentioned other than Ice, which is horrible for other reasons I will get into. On top of all of this, Electric encourages EQ or Earth Power, which, contrary to what has been stated, is not going to just be used "regardless", particularly with Togekiss in the wings. What about things like Earth Power from Heatran (versus Fire Blast), EQ from Gyara (versus Waterfall), or EQ from TTar (versus Crunch/Stone Edge)? None of those pokemon would take a risk to hit CAP11 with EQ when they know Togekiss will be waiting for it, unless CAP11 has a weakness to it, hopefully tantalizing out EQs, and thus providing switch-in opportunities for Togekiss.
One other major thing that seems to be gleaned over here is that Electric gives a resistance to Bullet Punch Scizor, a huge threat to Togekiss, as well as the most used pokemon in the game. In fact, it is this fact that makes Electric (or any other type that resists Steel) a much better typing for CAP11 than any other, simply because Rotom-A is largely irrelevant if CB Scizor can waltz in and nail both 'Kiss and CAP11 in the kisser.
When you add to this that Electric takes away none of Fighting's defensive gains, it is clear Electric is an excellent choice from a defensive standpoint.
Offensively: Again, everyone here is complaining that Fighting/Electric doesn't scratch Rotom-A. Again, I say...why is Rotom-A such a big ass deal? Maybe people are forgetting that we made Fighting the main type specifically so that 'Kiss can run attacks other than Aura Sphere? What attacks? Maybe....Shadow Ball? Another pokemon that people are complaining about is Gliscor...which is why so many pokemon run HP Ice. CAP11 will not have ridiculous offensive coverage with Fighting/Electric, but it will have plenty to do what it needs to do, which is support Togekiss. Also worth noting is that making it an Electric type will guarantee it gets TWave, with which it can cripple Zapdos or Rotom-A in a pinch if it needs to. No other type guarantee this kind of Offensive support to Togekiss, yet this is also being largely ignored.
Now, to why many of the other types suggested here are not ideal:
Ice: What was the point of making CAP11 a Fighting type if it doesn't end up resisting SR? Apart from this, Fire type attacks will rip the duo to shreds (Togekiss hates eating Heatran Fire Blasts), Scizor Bullet Punch will do the same, and any Fighting type can simply spam it's STAB move of choice and nail either partner in the duo. It even allows Rotom-A to hit it hard with Overheat. Simply put, this is a disaster defensively. Offensively, it' not a bad choice, as it hits Rotom-A neutrally and Zapdos Super Effectively, but other than that, it's not exactly working wonders. It invites all sorts of bulky waters in to wall the duo (I agree that bulky waters are not a huge concern to Togekiss, but it's not like they are easy to waltz by either). Overall Ice is slightly better than Electric offensively, but it also doesn't guarantee (and even probably rules out) TWave, which is huge for Togekiss to get off Nasty Plots and Roosts. Overall, the offensive capabilities of Ice do not make up for it's defensive and supporting shortcomings.
Dark: Defensively not bad, but not great. Gives CAP11 a nasty Fighting weakness while not giving it any notable resists apart from Ghost, although it allows CAP11 to maintain it's SR resist while making CAP11 harder to trap (by giving it a resist to Pursuit). Offensively, allows it to trap Rotom-A, and...not much else. Overall, kinda average in both categories, I would support Dark if it resisted Scizor's Bullet Punch, but seeing as it doesn't, I just can't see how choice "Rotom-A" (which is what it should be labelled) is better than Electric.
Water: Defensively, patches up the Ice weakness in exchange for making the pair weak to Thunderbolts. Rotom-A will walk all over this duo. Offensively, Water is not a great attacking type and never will be. At least it keeps the SR resist, but not much going on here overall.
Rock: Contrary to most concerned with Rock, I don't think the Fighting weakness is a big deal. What is a big deal is the Steel weakness. As I have already explained, CB Scizor gives Togekiss all sorts of problems already, do we really want to make Togekiss' partner further encourage Scizor use? Offensively Rock is decent, except for the fact that there are no good Special Rock moves, making NP Passing much less viable, while the even the best Physical Rock moves have subpar accuracy (Stone Edge, Rock Slide). Overall, the weakness to Bullet Punch just seems too problematic.
Psychic: Nailed by Rotom-A, nailed by Pursuiters, nailed by Scizor, nailed by Heatran, nailed by Jolteon...
Ghost: See above. Seriously, why are these two even being considered? Fighting is NOT a big problem at all for Togekiss, and making it's partner weak to Rotom-A and Pursuiters is just not the answer.
Now then, before someone says something along the lines of "But just slap Magnezone on your team for Scizor!" or "Just slap Suicune on for Heatran!" Let me remind you that I could just as easily respond "Just slap TTar on for Rotom-A!" You can't take any pokemon into account in this decision other than Togekiss and CAP11.
With all that said, I wish you, Fuzznip, and everyone else writing off Electric as "An electric resist and that's it" would reconsider Electric as a viable secondary typing. It's not exciting, and it is predicable after the last poll, but it is by far the best defensive option with Togekiss, and the best supporter due to TWave. Add in that we picked Fighting specifically to help Togekiss on the offensive spectrum, and it seems clear to me that Electric meshes extremely well with Fighting. Thanks for your time and for reading this (if you did), and please just think through this, it's not like there is a "right" choice here, so no need to flame others.