I'll predict right now that the techies will say 'marketeers' and the non-techies will say 'developers.' Just a hunch...
Marketing, hands down.
Marketing is a squishy job. It's hard to define, measure and hold accountable. Coding is a lot easier to define, measure and hold accountable. Bad marketing will only show it's ugly head once the product is launched and there is zero sales. Bad code (or engineering, take you pick) jumps out at you. If it looks bad, performs bad, then it's bad engineering. You don't even need to be an engineer to see that.
Caveat: This is coming from an engineer turned executive who has seen a lot of bad marketing. So much so that I can't help but be a little jaded.
Here's a slightly different answer. (BTW, I have a marketing degree, have been a developer for 10+ years, am currently in a sales & marketing role, and have had to hire for both roles.)
The answer is: It depends. It depends on your market, geographic location, and recruiting resources.
Here's a very unscientific & anecdotal example: I'm located in Silicon Valley, where there are a large number of both marketers and developers. When I posted job listings for both roles, I received almost 2x more resumes from marketers than developers. However, after weeding out the unfit candidates, I had roughly an equal number of potential candidates for both roles. (Caveat: I posted these listings on different niche job boards aimed at each particular role.)
Both roles also have specialties that will vary their hiring difficulty. For example, finding marketers with social media experience netted me tons of resumes. But only a handful had experience beyond "using Twitter and Facebook all day." Finding LAMP developers gave me a deluge of resumes, but I only found a trickle of AJAX developers.
I strongly suspect that my experience would be totally different if I were in Seattle. Or Colorado Springs. Or Bangalore.
My 2 cents.
I see this as industry dependent. So development and marketing occur in almost all industries together but the need for a stronger skill set is different based on the industry. In general industries that are long estabilshed are easy to predict and so the marketing of the industry is established. In industries that are emerging or in rapid change then the marketing smarts required to adopt is far higher. So say old school department store brick and mortor retail which is an old business or banking again an old business the marketing is "easy" compared to keeping together legacy systems with emerging technologies so operations can to use the information systems they need.
Chris is at least half right. I'm a techie and I say marketers with a few caveats. It comes down to subjective versus objective evaluation. I can give a developer a code test and determine objectively if he knows how to code. I don't see how you could test a marketer in the same way, at least without some kind of trial employment period.
Without being able to give the person an objective test, it comes down to past performance which means prior jobs and references. I still think evaluating a coder's prior work is more objective, but the longer the track record of success, the more it evens out. I don't see much difference in evaluating marketers and non-coding technical people like a CTO. Of course, I don't think I'd hire a CTO that didn't code for a startup.
Also keep in mind that marketing for a large company versus a startup would seem to be a bigger adjustment than coding for a large company versus a startup. I've coded for both and, while the working environment is different, code is code.