Defiant
Unlike other Starfleet ships, the Defiant-class is primarily designed for military purposes.  It was developed in order to fight the Borg.  Besides conventional weapons the ship has pulse phaser cannons and quantum torpedo launchers.  While further ships of this class have been built in the meantime, the USS Defiant was probably the only one with a Romulan cloaking device and was still in experimental status at the time of its destruction.

It can be supposed that the Dominion threat was the incentive to continue production of the Defiant-class, although the prototype ship does not meet Starfleet standards.

Most visual evidence points to a length of 120m.

The Defiant has landing struts, but thye have never been shown.  The real-world reason for that is that the producers didn't know that there were landing struts visible in the MSD.  In a fictional sense it may be questionable if the ship is capable of atmostpheric flight and landing on planets, since this would have been an option in a few episodes, so why was it not even mentioned?  It could possibly be that the relatively small Defaint was designed to use the shuttlebays in starbases.

The USS Sao Paulo was renamed in honor of the destroyed Defaint (DS9: "The Dogs of War") and should have kept the registry NCC-75633.  Unfortunately the ship was only seen as NX-74205 in "What You Leave Behind" due to the extensive use of stock footage.

There were two Defiant-class ships in Voyager: "Message in a Bottle".  Fortunately we couldn't have a closer look, because they were both labeled "USS Defiant NX-74205".