Marketing and public relations professional specializing in technology startups. Worked with 25+ tech startups around the world.
One way you could figure out what you want to do is to recap what you each did first and then figure out if there were any gaps in the offerings. So, "I was a developer, but my clients always wanted X." or "I was a designer, but I wish I had X." What tools did you each lack? What did clients want in addition to the service provided? If you find a common ground here then you're creating a business that is really needed in the market instead of replicating what's out there already.
The answer probably comes down to resources. Do you have the budget and staff to go after both segments? Each will need a different sales and marketing campaign so this can sometimes be daunting when getting up and running.
If you need to pick one, which one proved your concept? Which has a stronger buyer persona? Which do you offer more value to? Also, which one can you monetize. If you're choose the same segment for each of those questions, then you have your answer.
If you have the time and resources, a combined marketing and sales approach would really deliver. Ideally - these people and/or teams work together (which drives much higher results).
Sales - Cold emails do work. My advice would be to keep copy short since people don't always read cold emails and they certainly won't read long ones. Develop a clear sales funnel as well and create marketing content along the way to push people down the funnel.
Marketing - Marketers help bring in marketing qualified leads (MQLs) that sit at the top of the funnel. It's sales' job to push these leads down. Marketing techniques that I think would work would be social (LinkedIn is your best bet here), content such as blogging (get something for Google to read to rank you), and even email if you have a list or want to start developing one. The best rule of thumb for a marketing campaign is to provide the potential leads VALUE. Don't start with the hard sell, give them content they can use, find trustworthy, and want to share.
Happy to chat more!
In terms of who to target first, it'll likely have to be the free users, just to build a base. As you add on more features, these users will likely be open to paying for them. For platforms to launch/market the product, it's important to look at the buyer persona. Where are they/what platforms do they use? You'll want to be on the same ones.