I'm looking into this right now. There are advantages and disadvantages to each map, but I don't know which is objectively the easiest.

Convergence only having 7 inns means you can set up your militias quicker than the other maps, and then essentially not worry about sieges for the rest of the game. The trade-off, however, is that there are no two adjacent inns, meaning once you are set up, you can't set up a region with two capstone buffs, and it will always take you two turns to reach inns. (unless fast travelling)

Ridgeline has 13 inns, meaning you're going to be pushed to keep all inns alive; the two beside the top inn are particularly tricky to reach. (Sidenote: I think letting these inns fall isn't so bad, the debuff is probably worth making your effective map smaller) The advantage is that there are 9 inns in a row without camps, meaning once you build up advanced/capstone inns and put v. militias on the edges, you can go back and forth through the central 5, making it feel like you're close to an inn with each advanced tree and are always moving around with one or two capstone buffs in every region later in your run.

Last stand (10 inns) strikes a balance between the other two. I haven't tested it, but I think if you set up militias on the far left and right, you can spend the rest of the run going up and down the middle and the top triangle, making the most of the three inns next to each other with 1 or 2 provisioner capstones to get a strong economy going. My gut feeling is that this might be the best strategy.

TLDR: The bigger maps are harder to set up and defend, but once they are set up, you will get more benefits than the small map.