One of the things I wanted to do, is not make ships that could have been a predecessor to TNG, rather more of a TOS feel. I also wanted a clear tech progression that could be seen in older ships that would still be around during this age. Ships that were amongst the first warp ships designed are still in use since the technology is still relatively new. So, I started with a Warp 1 ship, the first Earth attempt at a production vessel with Cochrane's engine.
The Soyez Class: NX-1


First Earth Warp ship, launched in 2075 little more than an old design with warp engines strapped on. The huge fusion engine on the back both powers the ship's STL, and the warp engine. The designation of NX-1 denotes a Warp One capability, or 1x the speed of light.
The Columbia Class, NX-3



Developed in 2113, the Columbia utilized the warp three engine and really opened the stars to Earth. Capable of 9x the speed of light, Earth could send research ships along with freighters to near by star systems.
Hydra Class: NX-3


One of the projects to increase warp speed above warp three, the Hydra experiment added more warp engines to get more speed. While mildly successful, it never got past warp 4 and greatly increased fuel consumption.
Aegis Class: NX-3



Earth's Starfleet was rudely made aware of the lack of combat ability with the Columbia Class ships when Nausicaan pirates attacked and looted Earth colony ships and freighters. Nausicaan's destroyed three Columbia class ships when they were sent after the pirates. While work on more powerful ships was in process, a quick solution was to convert current Columbia class ships to an Aegis upgrade with more weapons. By the Earth Romulan War, all Columbia class ships, except a training ship, had been converted to Aegis configuration.
Daedelus Class: NX-5




5 years before the start of the Earth/Romulan War, Starfleet launched it's NX-5 capable ship, the Daedelus. Capable of 125x the speed of light, the new vessel could truly patrol Earth space and respond to trouble in hours instead of weeks. The new Antimatter engines also provided range, so that Earth ships could further push back to boundary's of their knowledge of the galaxy.
I know, I committed ST treason by redesigning the Daedalus, but I rather liked it. :p