Cubanos (or mixtos as they're called in Cuba and Miami), with their meaty/tangy blend of roast pork, ham, cheese, and pickles, have a pretty secure spot in the list of top 10 sandwiches of all time. It can be pretty tough to find a great one in Manhattan, but Havana Central does it up right. Thinly sliced but thickly stacked ham, well-melted Swiss cheese, a smear of mustard, plenty of sharp pickles, and really great juicy roast pork come together inside a grilled Cuban roll, pressed down firmly until everything is compacted and easily bite-able.
I often find sweet potato fries to be either too dark or too limp. At Havana Central, they're neither. Nice and crisp with plenty of sweet potato flavor. At $12 it's a tad pricey for a sandwich, but it's a big one (I couldn't finish mine in one sitting).