I'd recommend both. That's what I've done, and I've never hurt for work.

The thing is, many marketers offer lots of ideas, but are unable to implement the solutions. This means that a client has to hire a marketing consultant to create a plan, and THEN hire a designer/developer/etc. to actually implement that plan. This, to many clients, feels like paying twice.

Many of the people I've met will value development over marketing, and therefore cut corners on the marketing budget. This is bad news when you're a contractor who relies on other contractors or teams to build the things you offer as a service.

However, by building the skill set to not only design a marketing plan, but implement it as well, you're now able to market yourself as a 2-for-1 deal. As a freelancer, this is HUGE, because it creates a higher perceived value, and allows you to charge a higher rate. (They only need to hire you, vs. two separate contractors who will likely take longer overall to complete the job due to meetings, etc..)

Web development is the easier role to land early contracts. There are far more small projects for web dev; marketing tends to be a bit harder to break into (in my experience).

So for quickly building a stable income, start with web dev — but always continue learning. Every skill you add to your toolbox means one fewer contractor your clients need to hire, and that means happier clients, faster turnarounds, higher hourly rates, and a better overall experience for everyone involved.

I've been adding skills to my repertoire for over a decade now, and I bill my services as a one-man research and development team, because I can plan, design, develop, market, test, and manage a new business idea on my own. It took a lot of work to get here, but I'm now able to effectively write my own ticket because I can offer so much value and experience to my clients.

I'd be happy to discuss specific strategies if you'd like to put together a career development plan. I coach several entrepreneurs, and I think I'd be able to help you hit the ground running. Let me know if you'd like to schedule a short call.

Good luck!