I'd say - take metamidion ( gatling - mortar: mortar on the left, balloon side, gatling on right for the gunner). It's fairly easy to use, and in my opinion it's easiest to get some basic concepts of playing this game: teamwork (example: mortar must shoot only right after the red hitmarks start to appear, signalizing the armor break, thus - having enemy ship's permahealth exposed), communication (between the gunner and balloon engie), positioning aboard the ship, and by this I mean - specific areas players are responsible for (main engie - lower deck only, which means engines and hull, gunner - his designated gatling gun AND NOTHING THE FUCK ELSE, balloon engie - taking care of mortar, thus killing enemy ships and balloon to keep you up), and it's also fairly easy to position as a ship so you can hurt enemies. What's more - both of those guns generally requires greased for higher DPS, and maaaaayyybee some lesmoks for longer range if your mortar engie can't hit, THOUGH i'd discourage taking lesmok.
Mobula is tricky. You SHOULD learn the basics of how mechanics work, get to FEEL the steering of ships in general, and how to use pilot tools so you won't fuck your ship up too much (this is also a good test for the main engie, to keep those fucking engines up while pilot is maniacally burning down moonshine).
Well piloted mobula is a bloody killer. But if it's not piloted well, it's ill equipped, or the crew does NOT have common sense and don't know how to operate on it - you might as well easily get killed, despite it's cruel firepower potential. There's a reason why it's described as "Hard" to pilot in the ship choice screen.