So little information per your play style and where you are going in the game. PvE or PvP? The conversation totally changes with this answer. For PvE credit wise a slightly G3 engineered Python and allied with many factions near your home base will efficiently pay for every ship in the game with cargo missions in boom states. Then add a trading Cutter and the credits just start rolling in.
Corvette - Combat as the most maneuverable of the big three. When properly outfitted great for all those massive kills needed to get to combat Elite status. A little less grinding.
Anaconda - Slow and cheaper combat but amazing at exploration. Better weapons placement versus the Corvette. Great for passenger runs which also pays a lot. It's a big Python but slower.
Cutter - Amazing trader but with engineering and pilot skills will take on any opponent. Awesome shields. No other single ship can mass lock it. Being good at FA off is required.
Here is my engineered trading
Cutter. With so many options in the game it is different for everyone. See if that is where you want to go...