koth_bagel is a map I've always found very fascinating and effective.
If you want a quick summary of my thoughts on it, you can read the review I left on the map's page three years ago.
You can also take a look at my (rather unpopular) map
koth_slums, where the focus was on having a point area with interesting and limited cover, and on having very separated areas of the map right out of the spawn gates, so it's not as easy to spawncamp as your typical KOTH map.