There are many factors involved here.
Say theoretically that you had an A class Starport that you could produce a Imperial Navy warship design with, with the goal of making a profit, what type of ship would you produce? And I mean produce as in a fat military contract produce. What kind of ship would you get the most bang for your credit?
It's going to depend on your costs to produce each vessel. We don't get a lot of guidance about actual profit margins in canon material, nor do we get any guidance on IN procurement rules. If they give you a "cost-plus-percentage" deal, then you'll want to build the craft that has the highest cost per dton, which will probably be a heavily-armored craft. If the Navy pays "X credits plus cost" per dton, then you're going to be looking at whatever is going to get them out of your yard the quickest, and that's probably going to mean building fighters.
The construction time is going to be very important, too. You're looking to maximize the profit generated by each ton of yard space. if that ton of yard space generates 100,000 Cr of profit when working on a DN, but it takes 5 years to build it, it's only generating 20,000 Cr per year. If that ton can generate 30,000 Cr of profit when building a heavy fighter, but it only takes one year to complete, it just generated 30,000 Cr in one year. Repeat the process five times, and you're generating 150,000 Cr of profit building fighters versus 100,000 Cr of profit by building dreadnoughts.
(I'm making up these numbers for illustrative purposes -- I don't recall any specific costs per ton or any construction times off the top of my head, and it will obviously depend on the ruleset you're using to generate those numbers.)
Until you know what the procurement policy is (which is obviously a GM call), and you've finalized your designs for costs and times (also GM calls), you won't be able to give a definitive answer on this one. It's also going to depend on whether you can get enough repeat business on smaller craft to keep the yard generating income (and presumably profit) for as long as if you're building a big ship.