After a slight wait: The Colonist-3
The third of its line, the Colonist-3 is a much more advanced rocket than either the Colonist-1 or 2. The first two rockets were at best test runs for the flags and the communications abilities, but the Colonist-3 has been fully refurbished with an all-new transport vehicle that carries more than twice as many flags with far better maneuverability. The Colonist-3 has been purpose-built to plant a flag on Mercury, Venus, Earth, the Moon, the Captured Asteroid, Mars, Phobos, Deimos, and Ceres in one flight. Because of the balance issues cause by having the flags housed on the edges rather than down the middle (like the first two Colonist rockets did), the Colonist-3 is equipped with one port in the middle that can be used to hold an excess flag that would otherwise impact the center of mass of the ship
The route I used was Moon (only flag went, main ship did grav assist) -> Ceres -> Deimos (only flag went, main ship stayed in Mars orbit) -> Phobos (only flag went, main ship stayed in Mars orbit) -> Mars -> Venus -> Mercury -> Captured Asteroid (only flag went, main ship stayed in HEO) -> Earth, but I finished with over 75% of my fuel remaining, so you can go in any order you want
Needs Procedural Parts (SFS.S9), Hopiter's Nuclear Engines (Hopiter, just mobile version), PicoSpace Industries' Utility Pack (PicoSpace), Interplanetary Tech (jsudo, makes the main rocket look better but not required), Type Box (Kugelblitz64, just labels the flags), and probably a few other texture packs (Several of the ones I use have repeat textures, so I can't tell which is which)
Bp under mod comment
Expect a bit of a longer wait until the Colonist-4 because I don't want to re-use this rocket like I did with the Colonist-1 and 2, I also don't know exactly what I want the 4 to do other than something in the outer four