If I’m going to draw maps, I want them to be old school maps. Black lines, graph paper, no shadows, no textures. You can pretend this is because I am unartistic if you like; you will be correct in large part. Still.
Just about nothing does good old style maps. Dundjinni is really oriented towards neat battlemaps. RPG Map Maker is unpolished and is a paint program rather than a draw program. Map Tools is nice but is also more of a paint program, I think.
So OmniGraffle. You can set up a nice old school graph grid and you can include that grid when printing or exporting images. Snap to grid is easy. If you do everything as lines, it’s not too hard to add a hole in a wall. I figured out how to do round rooms. Caverns and river lines may be hard, but I’ll cross that obstacle when I come to it.