As we all know that the original Constitution class from the early 23rd Century had smooth surfaces and old warp nacelles. Then later got an refit to her design that carried the same name and registry number, USS Enterprise NCC-1701-A and I've been working on 3 other variants of the same crusier which are based in the future of the Federation also Starfleet.
USS YORKTOWN NCC-1717-A is the 1st newest variant slightly after the refit variant. With new design warp nacelles similar to marcusstarkiller's design of the Dominion wars. Also this design includes a Mark-1 Impulse engine of the late 23rd century design. It also kept the saucer design of the refit but until the construction of the 2nd generation ships things are changing.
USS TOM HANKS NCC-1970 is the 2nd generation variant created in the mid 24th century and was used for deep space exploration, with the Mark-2 Impulse engine the Constitution class variant II is faster than the original refit. Even the Bridge designs are slightly newer than a Galaxy class bridge.
USS SPITFIRE NCC-1944 is the 3rd generation of the mid 25th Century with better designs than the Soverign class starships. Alot better than J.J. Abrams Enterprise with the Mark-5 Impulse engine which makes the entire ship run silently at Impulse speed. The Variant III has brought together the entire galaxy for peace and friendship which set in the early 26th Century also the Spitfire was decommissioned for it's hard courage to bring all 4 quadrants of the galaxy together.