Hey... so yea I'd be fine with either really. One is a bit harder, but honestly if you know your stuff all you need is to pony up a bit and go take a test at a kiosk and be done with it. Take both if you can afford it and have time. I knew what both tests covered over the other so I'd usually ask a question specific to each cert to see if you're full of hot air, but otherwise none of it matters in the long run.

Here's the thing though, unless you are networked (see what I did there :D) and I have a heads up from [insert: aunt/uncle/friend-of-a-friend] I'm not going to be pushing for you with HR to be interviewed. That means you need to meet the resume requirements for one simple reason. At my job all senior security positions list CompTIA sec+ as preferred, along with some other certs. It doesn't list CCNA Sec. Why? Hell if I know but I doubt HR would listen to the CIO for stuff like this.

Regardless, if you don't have one of those certs and you didn't have someone say " I want an interview with that guy," then HR will just ignore your application. If you do, you'll be interviewed by HR first along with everyone else. Pass that, basically don't be a mouth-breather, then you move to the real interview with IT departments. This pertains to all areas, DBA/web/Linux... not just networking.

Now, I also look at senior security positions as more esoteric. You're going to be doing policy and procedure just as much as firewalls. So I do look for older, more experienced people there. With the CCNA you're looking at junior level positions, security isn't the primary focus. So maybe you're just looking at positions that people really are looking for a bit more experience? It's not so much you can't be trained, but more along the lines of "I want someone whose seen stuff Man". FWIW, our associate security positions don't require certs, which mean no HR gateway. In such a case, you'd be interviewed and if you were good we'd start you off a bit higher hoping to transition to a senior security position relatively quickly... and damn the cert.

P.S
I'm not in that position anymore, more suit less geek nowadays :( But I'm pretty sure things haven't changed that much. And obviously YMMV with other Orgs/Firms. Another trick with large corps is to interview for that junior position, show your security chops and tell them that's your main interested but you didn't want to flood the department with applications and risk being rejected outright.